Hi, I've just played "Scared" (http://www.brackeen.com/home/scared/index.html). It's a first person shooter a la Quake in a JavaApplet. It's the best Applet I've ever seen. The author is Dave Brackeen, the author of Developing Games in Java. Check it out, it really changed my conceptions of how fast an Applet can be.
This looks and feels so much like the software from an old Doom-era book I have, "Amazing 3-D Games Adventure Set," by Larry Myers, that I wonder if the author learned the mechanics of 2.5D FPS operation from that self-same book. Fun stuff, indeed.