[goofyballer]

Oh, duh, and Morrowind (prequel to Oblivion). Awesome awesome awesome awesome game, one of my favorite ever until I played Oblivion. You can prob pick up game of the year edition (game + its 2 or 3 expansions) for like $20 and then kiss 150+ hours of your life goodbye.

I think Morrowind was better than Oblivion in a lot of ways (gameplay mostly), so even if you've played Oblivion I think there's a ton of things Morrowind does better (most notably story and difficulty progression) that will keep it fresh and fun. I imagine the graphics are even still pretty good too.

EDIT: I remembered playing Psi-Ops on Xbox and thinking it was pretty fun, and its Wikipedia page says it's available for PC. Definitely a console-styled 3rd person shooter but I liked it. Same story (I played on Xbox but supposedly available for PC) with "Beyond Good & Evil", fantastic adventure game, I really felt in touch with the story by the end of it.