The Sydney Morning Herald has put together what essentially amounts to a "top 5 PC games from the past 10 years" article. There are a couple of obvious omissions, but at least three of the five are role-playing games: Baldur's Gate II (#4), Diablo II (#2), and Deus Ex (#1).
Part shooter, part role-playing masterpiece, Deus Ex typified the depth of gameplay that only a PC could offer at the turn of the century. Aside from maybe System Shock 2, it's hard to think of a PC game since that has offered the same level of immersion in both story and hybrid gameplay though many have tried and failed. Even its sequel fell short of the mark.