I am replaying the original Unreal single-player. Twelve years later the graphics still look good to me. A lot of people think this game is boring, but I think it has great atmosphere and music.
I have also started playing Elemental: War of Magic. It is a new 4x game from Stardock. The learning curve was a bit steep and first, but I am starting to have a lot of fun now that I am getting the hang of it.