oblivion, easily. not only because of base gameplay and all the extensiveness, but also because of all the mods you can download and all the extras in the special edition i got. But also you can make your own mods. how great is that?
I would have to say CoD2 Online. Dead Rising. And Gears of War. Maybe Burnout Revenge because of all the crashing.
I have throughly enjoyed Gears of War, due to it's online mode. The campaign mode is a lot of fun, but it has little replay value. But the online modes...as I said, throughly enjoyable!
The best game was either Battle for Middle-Earth 1 or Carmageddon 3. I will buy Zelda: Twighlight Princess and then I will have a new favourite I think.
I rarely buy games, most of them are FIFA and I have one NHL and Ghost Recon. I would pick Ghost Recon. Hours of fun.
Mine would easily be Oblivion for all the side quests and updates and lots of extra npcs being added makes it last ages. And takes up many hours of my playing time.
Super Mario World - I played it so much as a kid you just keep goin back and finding more treasures and ways to beat it Other than that Call of Duty series spent alot of time playing that for PC Medal of Honor frontline- Single Player greatness Socom 1-2- Great PS2 Online action