Game of the decade? Tough one. A lot of titles come to mind.
Perhaps Morrowind, San Andreas or Counter Strike (it was released in 2000 as a full retail game)
- Morrowind is a lot better then Oblivion IMO. I like the old text reading thing and the story was a lot better. I've spent more then 500 hours playing Morrowind and I didn't come even close with Oblivion. Huge modding fan base made it even better.
- San Andreas is one of my favorite games of all time. Best GTA game, great setting, great story and awesome characters. A blueprint for future free roaming games.
- Counter Strike: I still play it more then any other game. I still buy equipment (mouse, headset, mouse pad) just for playing CS and I still enjoy it as I did the first day I played it. It never gets old for some reason. And it's pretty much a cult game now.
Game of the year: Quite easy really, Batman Arkham Asylum.
Why? Best comic book game I've EVER played. Serious dark story well written, mature comic book faithful characters, dark setting, great combat gameplay, great stealth gameplay, good puzzles, awesome voice acting, impressive visuals and physics, great sound editing, a lot of neat unlockables. Did I forget something?