This is basically just a copy of the style of the others, but they were very well done and every system deserves representation, so here are 20 games in 2007 that are good reasons to buy a DS. Note: FFIV and DQIX are not on this list because they aren't officially slated for 07 at the moment.
Pokemon Diamond and Pearl (Available now)
Might as well start the list with an obvious one. Pokemon Diamond and Pearl is the 4th generation of the second best selling franchise of all time. The style of the RPG is unique and unlike any other. The basic mechanics remain pretty much the same, though this game evolves the strategy some by dividing attacks into 2 new sub-categories of damage type. The game adds 107 new Pokemon, and of course it's biggest feature: Online play. Pokemon has a global trade system (GTS) to trade pokemon accross the world. It also has the option to battle and trade with friends.
Final Fantasy Crystal Chronicles: Ring of Fates
As the title suggests this game is a sequel to the Gamecube title. The new installment of Crystal Chronicles will use a similar control scheme to the GameCube version, with A to use Commands; Y to pick up items (and allegedly enemies); and the B button to jump (which adds a layer to strategy, with multitiered levels in the 3D environment). Most of the gameplay takes place on the top screen. The touch screen shows maps, as well as stylus access for your different weapon attacks. Special attacks have also been confirmed in the game. By pressing the right trigger button, the screens will swap allowing enemies to be attacked just by touching them with the stylus. If done correctly, chained attacks can be preformed. It includes a multiplayer mode for up to 4 players. In multiplayer mode, your class influences majorly on how far you will survive. Five character classes can be picked from including Warrior, Archer, White Mage, Black Mage, and a support class. Each has specific roles to be fulfilled in the multiplayer mode. It's a great game for RPG fans.
Final Fantasy XII Revenant Wings
This game is a unique combination of RTS and RPG. One year after the events of Final Fantasy XII, Vaan is now a sky pirate with his own airship. He is joined by Penelo, Vaan's navigator and friend, and other returning characters from Final Fantasy XII. A few locations in the Ivalice of Final Fantasy XII return in Final Fantasy XII Revenant Wings, along with a new setting: Lemurés. The game offers the chance to play as many old FFXII favorites along with many of the monsters seen in the world of Ivalice. Espers also make a return in the game with the promise that they will be more useful than they were in FFXII. The game has well drawn 2D sprites on beautiful 3D backgrounds.
Final Fantasy Tactics A2
The sequel to the popular GBA title Final Fantasy Tactics Advance. Although the game is not directly related to Final Fantasy Tactics for the PSone the two share many features, including a nearly identical combat system. This game takes place in the world of Ivalice from FFXII as well, and many characters from FFXII will appear in the game. Combat takes place on grid based terrain in a turn based fassion, similar to a game of chess. Each character can perform different functions during the battle, and the goal is to eliminate the other person's team. There is no word yet on a multiplayer, but whether a fan of strategy or RPGs this game is a blast.
Heroes of Mana
This game is part of the same series as the popular SNES game Secret of Mana. It is similar to FFXIIRW in that it is a combination of RPG and Real Time Strategy. The game supports a deep single player plot. There is no multiplayer but the game does offer downloadable content of new maps and new missions for the player. There is no WiFi multiplayer available.
It's a Wonderful World
There has probably never been a more misleading name for a game. This game does not have an American release date yet (though the Japanese one is July, so there is plenty of time for it to be translated and out in America this year), so I'm sorry if it doesn't make it in time. However, the game is just so intersting that I couldn't leave it off the list. It's a Wonderful World was developed by the same team that created the Kingdom Hearts series. The game is very dark, and about 2 protagonists who basically fight (for lack of a better word) demons. Players assume the role of Neku, a young empathic boy, who meets a young girl named Shiki; both are forced to play the mysterious "Death's Game" while monitored by the Shinigami Corp, and must complete it within the seven-day time limit or else be negated from existence. Neku's empathic abilities are essential not only to gather the clues needed, but also to detect the Noise, monsters that dwell inside people's thoughts and are a hindrance to the protagonists. Character designs are handled by Tetsuya Nomura, who brings his distinctive art style to the game, and Gen Kobayashi. It has a great unique art style.
Rune Factory: A Fantasy Harvest Moon
Yeah I'll admit the title is dumb but the game is anything but. I don't know how many people played the Harvest Moon series, which began on the SNES, but this is it's latest installment. Harvest moon is a farm and life simulator that lets you grow crops, raise livestock, explore and interact with a village, flirt with, date, and marry women in the village, have a kid, build and customize your house, cook, mine, chop wood, fish, go to festivals, bet on horse racing, and much much more. This game has all that, plus combat. Yeah, that's right: It's harvest moon with fighting. There isn't much word yet on the fighting in Rune Factory but judging by the solidity of previous Harvest Moon gameplay mechanics it will be stellar. There is also a much deeper story in this one, with many more RPG elements.
Spectrobes (Available now)
The 8th RPG on the list (a lot I know) is a more controvertial choice then my others. This game recieved mixed reviews, but I believe it is truly a great experience. Think of Pokemon in a Sci-Fi future environment and you will be somewhat near this RPG. Spectrobes are very mysterious beings that harness light energy to unleash amazing powers, making them the Krawl's mortal enemies. Spectrobes once roamed the planets of the Nanairo solar system in harmony with ancient men. For some forgotten reason they are extinct, but Rallen is able to reanimate them using the lab system on his spaceship. Spectrobes come in three forms: Child, Adult, and Evolved. They are also divided into three types: Corona, Flash, and Auora. Each type is weak to another and strong against another. Admittedly, the gameplay mechanics are somewhat simpler than Pokemon but it still offers a fun and interesting experience. Spectrobes also offers some DLC, with new spectrobes that you can aquire over WiFi after beating the game.
Mega Man Star Force
Bet you didn't expect the last of the 9 DS RPGs of 07 to be a Mega Man game. Mega Man Star Force is the spiritual sequel to the Mega Man Battle Network RPG series on the GBA. The game shares similar art styles and gameplay mechanics to Battle Network, but is considered a seperate series. Mega Man Star Force explicitly states that it takes place approximately two-hundred years into the future of Battle Network, thus placing it into the network timeline. Mega Man Star Force is an action RPG much in the same vein as Battle Network. It is rendered in an isometric style (sprites, views, etc.) during field gameplay, but its battle system is three-dimensional, with the battles being viewed from behind Mega Man, and movement restricted to only left and right. Since enemies have a much larger playing field, battle evasion seems limited, but the player is given a choice of techniques like shielding and homing attacks to keep battles balanced.
Mega Man ZX Advent
Advent is the 2nd game in the Mega Man ZX series (ZX is the 6th Mega Man series in case you were curious). This Mega Man game has 2 different story lines. The first follows Grey, a 14-year-old failed experiment that was recently awakened from cryogenic slumber. The second follows Ashe, a 15-year-old ruin hunter that works for Legions, a government organization that oversees world affairs. As with all Mega Man games the heroes have abilities and attacks that evolve throughout the game, in this case through the use of battle suits called Biometals. 
Custom Robo Arena
Who doesn't like battling with custom made robots? I know I do! Custom Robo Arena is the 5th installment in the Custom Robo series, and allows the player to contruct and battle with their own personalized robots. More customization options become available as you advance through the single player, but the real fun part is online WiFi battles. Pit your own custom warrior against your friends online in epic battles! A great and interesting fighting game.
Brain Age 2: More training in minutes a day
I know this game isn't for everyone but it deserves it's spot on the list anyway. Brain training 2 is exactly what it says it is. Brain games that challenge the player to think quickly. It's a good time passer and has limitless replay value.
Spider-Man 3
No this isn't a mistake, I actually did put a Spider-Man 3 game on this list. Why? This is actually a really great side scrolling fighter, despite the mediocrity of the other versions. It was well recieved (Getting an 8.1 from IGN) and is a blast to play. All combat is done on the touch screen through a variety of stylus motions. The graphics are crisp and well done.
Sim City DS
This game is a heavily modified version of Sim City 3000 (the good kind of modification, not the bad kind). The game inherits SC3K's graphics, but makes use of the handheld's dual screen to display additional interfaces at once. System specific features were also announced, such as the use of the systems' integrated microphone, which will be used to blow out fires.
Phoenix Wright: Ace Attourney (Justice for All and Trials and Tribulations)
Yes, I combined both 07 PW games into 1 entry, because I figured I would be criticized if I used the game twice to fill the 20 spots. The gameplay doesn't change a whole lot between the different games anyway, but the plots are always entirely new, and that's what Phoenix Wright is about. Phoenix Wright games are basically point and click adventures, but don't let that fool you: They are deep, challenging, and interesting adventures. The characters have great personalities and some are hilarious. Find the evidence you need to defend your client, then go to court and defend him by presenting evidence and interrogating witnessess. There isn't much replay value but the initial playthrough of any Phoenix Wright game is an amazing experience that should not be missed.
Hotel Dusk: Room 215
Hotel Dusk is in the same point and click mystery genre as Phoenix Wright. It has just as deep and engaging a story but it doesn't have the humor of Phoenix Wright. Still, it is an amazing game. It is also one of the few DS games that plays with the DS held like a book. Everythin in the game is run with the stylus. This game also has a very interesting pencil art style.
Planet Puzzle League
I know gamers seem to have a natural aversion to Puzzle games but this is a great one. It's like most puzzle games, but with a fun online multiplayer mode. If you don't like that I stuck a puzzle game on the list just substitute one of the 07 Phoenix Wright games lol.
Final Fantasy Fables: Chocobo Tales (Available now)
This is an adventure RPG made out into a series of mini-games, micro-games, and card games. The battle card game is used for boss battles and WiFi multiplayer. Multiplayer includes playing the card battles in multi-card and online play by using Nintendo Wi-Fi Connection, and the mini-games are multi-card and single-card download multiplayer as well. 2-4 players may team up for battles, or to participate in mini-games. Yeah, it's kinda kiddy but it's actually really fun. Especially the card game battles.
Lunar Knights (Available now)
Lunar Knights is a great adventure game that unfortuantely never got much attention. Lunar Knights revolves around two characters: Lucian and Aaron. Lucian (Sabata in Bokura no Taiyou DS) is a melee fighter, wielding the Dark Sword Vanargand (Ankoku ken Vanargand in Japan), the Dark Scythe Hel (Ankoku sou Hel in Japan), and the Dark Spear Jormungandr (Ankoku gama Jormungandr in Japan). He is also imbued with the power of darkness, and can change into a vampire after he builds up a Trance (shortened to TRC in-game) meter by fusing with his Terrenial, Nero, which allows him to absorb life out of his foes, a mechanic that debuted in Boktai 2 as Black Django. Nero is based on the cat of the same name in Boktai 2, who was rescued by Sabata many times. Aaron (Django in Bokura no Taiyou DS) is an apprentice sharpshooter, and uses a variety of Solar Guns to deal damage to his undead foes. These include the Knight (uses a Charge Shot, similar to the Gun del Sol), the Ninja (dual-wielded machine guns), the Bomber (explodes in a radius shot), the Witch (homing rockets), and the Dragoon (flamethrower). Unlike Lucian, Aaron has light powers, and can temporarily become an avatar of the sun when needed by fusing with his Terrenial, Toasty (known as Otenko in Japan, another reference to the original Boktai games), much like Sol Django in Boktai 3 (released only in Japan).
Legend of Zelda: Phantom Hourglass
I saved the best for last. I'm sure everyone knows what this is already, but I'll go ahead and explain it a little more. It's a 3rd person Zelda adventure (played from a semi-above view, similar to the old 2D versions). PH is the sequel to tWW for Gamecube. The gameplay in this Nintendo DS game is mostly overhead, similar to most 2D The Legend of Zelda titles, but the character models and the environments are in 3D. The rendering environment is similar to Animal Crossing for the Nintendo GameCube, and somewhat like the Nintendo DS sequel to Animal Crossing. The touch screen is used to show the main gameplay, used to control Link, or to solve puzzles (such as the hourglass shape at the beginning of the trailer shown at GDC), while the upper screen is mostly used as a map screen. The map can also be brought down to the touch screen, allowing the player to write notes on it. It will also be used to create a taller screen in some events, such as the battle scene in the trailer. All boss battles will use both the top and bottom screen. The microphone will be used in some way as well.
Edit: ResiRiley had a few interesting games that are certainly worth mentioning as well. So I'm adding them to the list. Sorry, I know it's not 20 anymore but who can complain about EXTRA good games?
Dementium: The Ward
According to IGN, Dementium: The Ward tells the tale of a man who awakens to find himself alone in a mysterious, derelict hospital that is frozen in time. Confronted by the deadly, grotesque surgical experiments that wander the halls, a series of challenging puzzles and a cast of peculiar characters, he must face his deepest fears, unlock the mysteries of the hospital, and escape with his life. The Ward takes advantage of the unique properties of the Nintendo DS system with touch-screen exploration, puzzles, and Wi-Fi multiplayer gameplay. Using the Nintendo DS touch-screen to look and aim provides the player with an enhanced sensation of freedom and control. The dynamic real-time flashlight immerses the player deep into the game's eerie atmosphere and allows the player to search the dark corridors of the hospital. Ninja Gaiden: Dragon Sword Again, the IGN info on this great looking game: Ryu Hayabusa returns in this action-packed and totally unique game following Tecmo's thrilling Ninja Gaiden series. The Team Ninja-developed title is a 3D action game that makes full use of the DS's most standout feature: the stylus. The entire game can be controlled almost entirely with the touch-based motions. You guide Ryu about the play field by tapping in the direction you'd like to go. Slashing the touch pen from down to up makes Hayabusa launch an enemy into the air, into a perfect position for combos. You make Hayabusa jump by tapping the screen twice, and can then point to enemies to shoot shurikens at them and perform a downward thrust attack. Even your ninja arts make use of the stylus, requiring that you draw shapes in order to perform the special attacks. Buttons are used only for defensive moves. As you can see the graphics on this one are very impressive. Obviously this is somewhat niche, but it is the first time we have gotten one of the games from this Naruto series of RPGs so it's certainly worth nothing. Choosing from six available characters, players are able to explore the Village Hidden in the Leaves and the world of Naruto as you roam across forests, fields, rivers and mountains. Along the way players encounter various bosses and enemies that they must use their special techniques to defeat. 
Naruto: Path of Ninja
