deliantra! (Score 1)

I love Deliantra http://www.deliantra.net/ very much, it's a bit retro-style and has quite some depth. At least I got addicted to it quickly... Another nice thing about Deliantra is that you can also make your own maps and monsters and contribute them. Also, in contrast to many other free online games, it's completely free software, and everything is available under the GPL. You can get the whole code and gamedata anytime and do your own stuff with it.