I'm "playing" the latest svn checkout of
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(a new release is due soon). The Quake 1-style gameplay is irritatingly simplistic, but the engine is impressive. In-game editing, an octree-based world structure, and it's open source.
An MMORPG based on this engine might be really cool. There was an effort to create a single player RPG, but it appears to be dead.
I'm still kicking ass on Street Fighter Anniversary Edition. Mastering Street Fighter 3 Third Strike. I am so good at it now I can use one hand and kick Gill's ass using Ken or Ryu!