Kinda a three way tie.
1. The Sims 2 (PC) - Ok, I know, but it's got so much replay value and extremely addicting. I have to put it on here. I've always liked simulation games and this is pretty much the peak.
2. Super Mario Galaxy (Wii) - Pure creativity, some of the best music I've ever heard, very addicting and extremely fun, plus excellent controls. This is really the only truly "amazing" 3D platformer I've ever played. I played some great 3D platformers, but all of them have bad flaws. SMG has pretty much none and defines the genre. Truly one of the best games ever made and definitely the best for this generation.
3. The Legend of Zelda: The Wind Waker (GCN) - This game is a masterpiece. It has some of the best controls I've seen in a game, the best graphics I've seen in the game, some of the best music I've ever heard, tons of sidequests, and a truly epic adventure, with an excellent story and ending. Pretty much the only reason to own a GCN.
If I HAD to rank them I guess
1. Super Mario Galaxy
2. The Sims 2
3. The Legend of Zelda: The Wind Waker
Top 3 favorite games: Super Mario Galaxy, The Sims 2 (PC), The Legend of Zelda: The Wind Waker
