Call of Duty 4 - 10/10 - Pretty much perfect.
Halo 3 - 7/10 - Fun multiplayer, but not something I could play forever.
Oblivion - 10/10 - This game took so many hours of my life.
Tiger Woods PGA Tour 2007 - 6/10 - Okay for a pickup-and-play.
Cabela's Alaskan Adventure - 2/10 - I seriously could not become interested at all.
NBA Street Homecourt - 7/10 - NBA Street games are always pretty good.
NBA 2k8 - 8/10 - Same as above.
Splinter Cell Double Agent - 7/10 - Didn't play it much, but the double agent thing is interesting.
Marvel Ultimate Alliance - 5/10 - Other than a wealth of characters, I don't see the appeal.
Forza Motorsport 2 - 9/10 - One of the best track racers I've ever played.
Dead Rising - 8/10 - Flawed, but fun and hilarious.
Enchanted Arms - 9/10 - Excellent story, but the difficulty curve is ridiculous and it's kind of unrefined overall.
Ninety-Nine Nights - 7/10 - Eh, I like Dynasty-Warrior style games but this wasn't anything special.
Saints Row - 9/10 - A couple things from San Andreas were missing that I liked, but a lot of cool new shit was added too.
Guitar Hero III - 10/10 - GET. THIS. GAME.
skate - 9/10 - One of the most refreshing gaming experiences I've ever had. You won't want to play Tony Hawk again.
Bioshock - 9/10 - This game is so gorgeous, and it's interestingly unique.
Marble Blast Ultra - 10/10 - The best Arcade game available, IMO.
Castlevania: SOTN - 9/10 - This was actually extremely fun.
Geometry Wars - 8/10 - A Robotron ripoff, but great nonetheless.
Band of Bugs - 6/10 - A decent turn-based strategy game.
Aegis Wing - 8/10 - A solid space shooter. Plus, you can't beat the price (free).
Yaris - 7/10 - It's like a game based on the secret ring levels in Sonic 2. Great game that everyone should have (also free).
Puzzle Quest - 8/10 - A lovely combination of Bejeweled and traditional RPG fare.
UNO - 5/10 - Relaxing, I guess, lol.
Alien Hominid HD - 6/10 - Impressive that a dumb flash game has gotten this far in popularity.
Boom Boom Rocket - 9/10 - Extremely fun music game. Guitar compatibility is like icing on the cake.
Bankshot Billiards 2 - 8/10 - It's nice to be able to shoot pool over Xbox Live.
Track & Field - 7/10 - Ahh, classics.
Hexic HD - 6/10 - Not bad, considering it came with the system.
Luxor 2 - 5/10 - For some reason I got this for free ?_? Not too bad, anyway.
If I think of any more games I have, I'll add them.