Roleplaying would a great start, although obvious. I recommend Neverwinter Nights, Baldur's Gate (don't let the bad looks turn you off) and Morrowind.
As for other games, Tiger Woods PGA Tour 2005 is quite great. I know it's just golf, but it is still quite fun. Tony Hawk's are also recommended, but I haven't tried them on PC. I love the PS2 versions, though. T.H.U.G.2 are far too easy, but other than that they are quite great.
Many sport games like NBA, NFL and that allow you to at least customize new characters, and the Street versions are even better and more enjoyable. Not sure if they are on PC, though.
Need for Speed: Underground 2 let you customize your car quite a bit, and is worth a check. On the other hand, I suggest you go with Midnight Club 3 instead. It's far better. Neither have characters (although you can select driver and outfit when using bikes in MC3), but they are still fun.