LogFAQs > #905462485

1) San Andreas (Casual missions, driving and killing people with guns just for the fun of it)
2) CoD 4 (Huge multiplayer game, my personal favorite is BO2 though)
3) Minecraft (Although it became massive in the post 2010 era, I'd still consider it a 00s game)
4) Mario Kart (And casual Wii stuff in general)
5) Oblivion (One of the major reason why open world genre became so popular)
6) WoW/LoL (Oh yeah multiplayer was the biggest thing of 00s for gaming)

Honorable mention - Although not as big as RBY/GSC, Pokemon's numbers and success is hard to ignore.
---

I say appreciate the life you have, because it can always be worse