Over the past week or so, I've played Skyrim (as an archer, I've not yet tried a melee (sword/axe/etc) or magic build), Perfect Dark (still the best game ever, the last time I played was me vs three teams of bots in multiplayer), and Singularity (first person shooter, sort of like Bioshock merged with Half-Life 2).
All great games, but with Singularity I felt like I was just going through the motions, as (like Bioshock and Half-Life 2, etc) the fact that it has so many memorable and scripted scenes unfortunately harms the re-playability, as you always remember what comes next.
Edit: I'm about to start Deus Ex (another superb game) with the mod GMDX 8 (http://www.moddb.com/mods/gmdx).