Here we go, nothing else to say. No particular order, again.
1. Fallout 2.
-Holy cow, the mother of darkly humored, in-depth RPGs. If you haven't played it, play it. Get it on Good Old Games.
2. Call of Duty: Modern Warfare 2
-Bitch as much as you want, this game is as close as you can get to a perfect (non-squad-based) FPS.
3. Pokemon Silver/Gold
-Okay, wait. I loved Pokemon Red and Blue, but they're just included in Silver and Gold. And shit just got made better. And they didn't turn all the Pokemon into gay robots yet.
4. Grand Theft Auto: Vice City
-Good gameplay, fantastic storyline. I don't go back to any game as much as I go back to this. Alternately, San Andreas could take this spot. I'd almost give it to San Andreas, but I hate having too much stuff to do for 100%. I am a completionist whore on video games, and San Andreas had way too much random crap.
5. Skate 2
-Not since Tony Hawk's Pro Skater 3 have I loved a skateboarding game this much. Excellent concept, worked spectacularly.
6. Metal Gear Solid 2: Sons of Liberty
-WHAT?! A sixth one? Yes. I can't go without including this game. The only good stealth game ever made, besides perhaps Thief.
Some honorable mentions include Unreal Tournament 2k4, Starcraft 1 and 2, Half Life, World of Warcraft (yes...), and many others. I should have just made a top 100 list. But there you have it.