I like a lot RPG games,
www.planeshift.it ---> opensource, free, still in development. Also i play windows games like Warcraft 3 with winex 3.2
You can download Neverwinter Nights, the version for linux ( nwn.bioware.com ) You to buy it, to enter the cd key or get a cd key and just playing in single player mode.
Nowadays a lot of company games are relesing a linux version.