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Since you've put some effort into this thread I didn't want to make a cheap list post like Andre 
So here goes:
Dance Central (XBox 360)
I've always been somewhat reluctant towards dancing games. Mostly because none of them felt like dancing at all and also because the tracklists were full of J-Pop. Then came along Dance Central for XBox Kinect, I saw the ads, I watched the youtube videos, I wanted this game ... bad! So bad that I bought a 360 just for this game. The game turned out exactly like what I've always thought a dance game should be, real dance moves and fun varied tracks to dance to. Playing alone it's a great workout (and you can try out the hard setting without anyone to see how you totally miss most moves) and playing with friends is an absolute blast.
Plants vs. Zombies (Game of the Year Edition) (PC)
BRRAAAAAINS! The Zombies are coming!
I had heard a lot of good things about this game for many months and it ended being the game I gifted to my Tiny Tim in last year's Steam Secret Santa (he had requested it). I was intrigued, so I decided to buy it for myself and what I discovered what a quirky, fun and addictive game. The game offers a great variety of plants to counter an equally varied army of invading zombies (Zomboni being my favorite because of the wonderful pun) and just when you think you've mastered the art of zombie killing, night falls and you've got to change your whole strategy.
You can also take a break from the main game to play a great range of mini games from zombie bowling to vase breaking to zombie-jeweled. Afterwards, if you're really looking for a break, there's the Zen Garden where you water your plants, feed them fertilizer and train a snail to collect money!
New Super Mario Bros. Wii (Wii)
A RED BOX!
That's my main argument for putting this game in my list but if you want more well there's the long awaited return of 2D Mario games (don't mention the DS game because handhelds don't count everone knows that). It features great level design, a SMB3-like map, fun power-ups, Yoshi, added replayability (Star Coin collecting) and most of all 4 player madness! It allows you to help out a less skilled player if you're feeling nice and if you're feeling naughty, it also allows you to throw your friend down a pit or take all 4 Power Ups and leave your friends with nothing .
Resident Evil 5 (PS3)
Did I put this game in my top 50 just because of the yummy Chris Redfield? No, I'm a real Resident Evil fan and I love these games for the gameplay first and foremost (but eye candy is always a nice bonus). The big change this game brings is the co-op gameplay which I really enjoyed. Especially when I got to play through the game with my brother who's much better at RE than the AI. The game also features the return of Wesker, my favorite RE vilain, in his quest for COMPLETE GLOBAL SATURATION!
In the end, what made me like this game so much is what I love about all RE games: killing zombies and huge deformed bioweapons. That and the mercenaries mode which is so addictive and thrilling!
Uncharted 2: Among Thieves (PS3)
Nowadays, I rarely replay games on a harder difficulty because I always have 2 or 3 others games waiting to be played but I enjoyed Uncharted 2 so much that I played through it 3 times (normal, hard, crushing). The story was very interesting, the characters were nicely presented and it didn't take long before you cared about them (well except for Jeff the cameraman, I didn't give a crap about him). Tthe gameplay was a nice mix of third-person shooting, stealth, (really really easy) platforming and puzzle solving. The locales you visit are simply gorgeous, the Nepal mountains and Shambala being my favorites. The game struck a balance between all its elements that just worked perfectly and kept me wanting to play it again.
Super Mario Galaxy 2 (Wii)
One of the best 3D platformer ever made. Although I had feared it would be feel too similar to the first Galaxy game, the developpers at Nintendo managed to keep things fresh with incredible level design , new galaxies that made great use of both the new and old power ups and the inclusion of Yoshi. Only some returning bosses keep this game from feeling entirely new.
The game has you rescuing Peach once again but I'm starting to think this whole charade with Bowser is planned just so Mario can collect stars without anyone asking questions and he then proceeds to sell them on the lucrative stars black market giving Peach and Bowser a cut of the profits.
While searching for the game's 120 regular stars you get to fight off a giant dragon, a giant beetle, a giant mole (anything giant really), you also get to use new power ups like the Cloud Mushroom which allow you to generate three clouds giving the freedom to get very high or very far or the Rock Mushroom allowing you to become a rolling boulder knocking down all enemies in your path and getting yourself killed by flying off the ledge.
Once you're done with collecting the first 120 stars, you get to search for the Green Stars (which is much better than just redoing all the stars with Luigi like in SMG). I really enjoyed that part because it reminded me of Mario 64 where you didn't always know where you'd find your next star and some exploring was necessary.
All in all, this game is 3D platforming like only Nintendo knows how to do and it's fantastic!
Donkey Kong Country Returns (Wii)
With this game Retro Studios have done the impossible: capture the essence of what made the DKC games so fun and manage to create a game that surpassed even the original. World after world this platformer comes up with new ideas making it fresh from start to finish. This time around instead of collecting bonus levels you get to search for puzzle pieces and KONG letters.
While I try to get as many puzzles pieces as I can, I really focused on getting the KONG letters because they unlock the incredible K levels in each world. These levels really test your platforming skills (and sometimes your patience ) but managing to finish them all is one of the most rewarding gaming experience there is.
Super Smash Bros. Brawl (Wii)
Over 400 hours of play time. More 6000 online Brawls. A fighting series like no other. SSBB is one of the reasons I became a frequent poster on this site, the Brawl thread was excellent to find opponents and to comment and whine about a heated match. Despite being mid tier at best, I never changed my main character and continued to kick ass with the mighty Peach. Of course, she wasn't the only I used Pikachu, Diddy Kong, Bowser, Yoshi, Ice Climbers, R.O.B. all got plenty of playtime.
I know the online mode wasn't all that great when you used to the "With anyone" option but with friends from VGChartz or Allisbrawl or Smashboards there's no other fighting game that even comes close.
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