I only tried to play HoN - the game did work and din't crash or had any performance issues - but there were many glitches and alt-tab not working made me give up. Most of the issues with stability I had were with Gnome 3 + closed source driver (Unity as well, but I haven't tried Ubuntu since 11.10 Alpha). I also tried to play some games with Wine and that didn't work so well (NvN, HOMM) - again random glitches and crashes.