Take a guess what OS this is running in:
If you guess Ubuntu 8.10 64 bit with no emulators, you'd be correct! That's a screenshot from Regnum Online, a free to play MMORPG that just happens to offer a Linux client. I took that screenshot from a cliff overlooking the battle before I stupidly jumped into the fray and swiftly died.
Here I am shooting my wimpy magic missile at the beast just before he killed me in one blow:
Regnum has been around for just over two years. It's not quite as in depth or polished as some of the games out there like Knights Online or Silkroad, but it's certainly an enjoyable game. They also have announced that they will be releasing a new upgraded version with better graphics and dynamic shadows in the very near future and that they do plan to continue to support Linux.
Kudos to them - they just go to show that there's no technical reason you can't develop awesome games for Linux. It's mostly political (and market driven,) but we knew that already.