Oblivion and Fallout 3 ( seems to be a trend here, despite their flaws there's just so much to do for the insane completionist in all of us ), Sins of a Solar Empire, and probably my most puzzling, 280+ hours in FFX, complete with an undefeated mostly level-99 Blitzball team.
Easy steps to own at Blitzball:
1. Recruit Shaami in Luca.
2. Put her in center position and make her learn all her shots and tackles.
3. ???
4. Win. Every game. Mr. Famously-Awesome-Blitzball-Player Tidus can't touch Shaami.
[Edit: forgot to mention a few others. RuneScape, back in the days before I knew EQ, which I never got into somehow, and Red Alert/Dune 2000. I miss Westwood, EA needs to stop prostituting their franchises.]