This is somewhat of a departure for me. I've been doing some work for my client that involves WebStart, a system that lets you deploy Java applications from a webserver without installing any local tools (aside from Webstart itself, natch). "A perfect avenue for games!"
So digging around, I started looking for games I could run via webstart (which, by the way, runs perfectly under Linux). I found Jake2.
Jake2 is a pure-java implementation of the Quake2 engine, from Id Software. If you have any interest in first person shooters, or haven't been under a rock the last 7 years, you've heard of Quake. I had pulled Jake2 a while ago as a standalone app, and it was 'okay', but a bit bumpy. Since I still had my Q2 maps locally, I was able to just click on the Jake2 Webstart button on Bytonics webpage, say "Here are my maps" and I was off and running.
The game plays perfectly, with a high frame rate on my laptop, and seems to handle many of the issues of running "a full screen app in a window" quite well (the mouse motion does NOT move the 'pointer' off the window, and you suddenly stop moving, easy prey for the nasties lurking about).
I also was able to download a couple third party game maps, and install them into the baseq2 directory, and run around a bit. Only one caused Jake2 to crash out, and that could easily have been because of a bad map. The Id supplied maps were fine.
Next on the list will be to try using the networking code, and playing multiplayer. Moohahah.

Linkie brokie.
Oops, broken link to Jake2 fixed.