R:FoM - The multiplayer component is what makes it stick out. 40 player online for a console game was, still is, pretty huge, and now we can expect 60, and an 8 player co-op.

Resistance 1 defined what a FPS should have for online console gaming, Resistance 2 will re-define it.

This generation has only been around for two years but there has been so many memorable games to come out of it.

Wii Sports - Showed that simple works and still continues to show that.

Gears of War - The first game this generation that really wowed me in the looks department and made third person shooters their own genre because of its excellent controls and cover mechanic.

Resident Evil 4: Wii Edition - Proved that the Wii controls can really make a game by being directly able to compare it other versions with still good but inferior control schemes.

Metroid Prime 3: Corruption - Yes, the Wii and FPS games are a perfect combination.

Zack & Wiki - Bringing back the point and click adventures. Nuff said.

Bioshock - Excellent storytelling. No game has come close to the level of story telling and the way it presented itself in years and probably won't be beaten for years to come.

Sneak King - Who would have ever thought a $3 game would take the nation by storm? This game was actually hard to find. WTF.

Lair - Proved that gamers really do want more than hype and graphics.

1. portal: completely changed what's possible in a game universe

Resident Evil 4 & Metroid Prime 3:Corruption-The controls and immersion they provided were simply amazing.

Mass Effect- The incredible dialogue and stroytelling were simply the best I have encountered so far on the 360.

Wii Sports- The first and only console game my mum have been interested in playing. It was also a brilliant showcase of basic but enjoyable motion controls.

Ratchet and Clank Future: Tools of Destruction: Just a really solid game, reminded me tried and true gameplay can still be really fun. Proved that platformers did have a place on HD Consoles. It also demonstrates ways to make a game fun through its gameplay.

Halo 3: Now I am not a Halo fan, but Halo delivered everything you would expect from a Halo game while expanding on it innumerably. It didn't bring in many/any new gamers or innovate much but plays to the other principle of this generation: Bigger. Better. More.

For me Wii Sports has been THE defining game. My first, and only game for a while, showed me the potential of the wii and wiimote. Simple movements in baseball and bowling seemed shallow at first, has provided me with hundreds of hours of enjoyment.

Another defining game, although to a smaller extent, was Metroid Prime 3. As someone who has had little experience with the Metroid, and Metroid Prime series, I was going to pass this one as well. However, watching the first hour on youtube, and seeing the on-screen cues which showed me that wiimote movement led to in-game movement, sold me on purchasing the game.

There have been other great games (Zack and Wiki, Trauma Center:NB, SMG, Zelda:TP, etc.) but none of these games have made as big an impact on this generation.

Portal: Design brilliance. This game was just a perfect amalgam of cleverness, humor, and atmosphere.

Zack & Wiki: Point and click revived? Hell yes! A brilliant puzzle/adventure game that really showed how the Wii can be different from the other consoles.

Metroid Prime 3: The firs time I've ever played an FPS (/Adventure) on a console and thought "Wow, this is as fun as shooters on PC." Now, before my fellow PC gamers shoot me, I didn't say it was a precise or accurate, but it was as fun. Absolutely incredible, and far above dual analog controls. The first next-gen console FPS controls.

Call of Duty 4 (PC): I used to be one of this game's biggest critics, but when I finally sat down with it, and got into the multiplayer, I was blown away. The single-player was like playing the best action movie ever made (also as short as an action movie hehe), but the multiplayer experience is second to none. Many have described this as the next counter-strike, and I think they are right. 50 man Team Deathmatch is insanely awesome, and this game really blew me away.

Super Mario Galaxy: Pure, untainted, child-like wonder is all that I felt as I played this game. It was simply an incredible feeling that I hadn't felt while playing a video game in at least 10 years. Thank you so much Super Mario Galaxy for bringing that back. Next comes Brawl!

@naznatips: finally, someone else noticed portal, haha. To be honest, now that I think about it, aside from wii sports, portal may be the only game that truely brought somthing brand new to the table. Games like CoD4 had masterful graphical and sound enhancements, halo3 1-uped internet play and galaxy and other wii games offered up some cool stuff. But in terms of that just "wow, that's completely different," portal and wii sports.

Although I don't have alot of experience with all of the consoles this generation, I will use my thoughts as well as experience to answer this one.

Gears of War (Xbox 360):

This game basically made everyon stand up and notice the difference between the last generation and this one by utilising noticeably much better graphics.

Wii Sports (Wii):

With the launch of the Wii came Wii Sports, this is the game that has brought everybody from all walks in life together to play tennis, bowling etc.  People normally not bothered by video games were hit over the head and dragged into the 21st century to enjoy some easy play, easy interactive gaming of the next generation.

Uncharted: Drake's Fortune (PS3):

What Heavenly Sword started on the PS3, Uncharted completed.  Truely next gen gameplay, visuals and true movie style interaction.  This game brought all these elements together to create the closest to interactive movies done so far.  The visuals have pushed this title to the very top of this generation so far.

When I was playing the full version of Heavenly Sword for the first time, I was completely blown away by the acting in the gameplay. The cutscenes were great, but the way the bosses lead the troops and talk during battle (with the little picture in picture). This may not seem like a big deal to anyone else but this was really cool. Overall the game was just good, but there were some really cool things.