I want to experiment with using Java as a language for graphics intensive games. I think that this could be effective with Java 3d or intensive use of JNI. Anybody have experience going either of these routes? What kinds of experiences have people had in general with writing games in Java?

Java3d is a good platform for beginners to start programming games. I myself started to learn Java 3d from spinning simple cubes to create user-interactive buttons.

The basic requirement of using java3d is you must have a good foundation of Java language before attempting to do so.

I personally don't like java, the litle quirks that can entirely tank your program really piss me off. I much prefer C++ more sense, and i dont have to worry about which classes can see this class or what object can use this method, etc.

I use java. I use a lot more application side of programming in java, but from my experiences with Java 2D and Java 3D, you need to know the application side first, which is basic coding with I/O. Then you can go to graphical interfaces and all the events. Everything you do in an applet is an event. some classes with the java compiler are abstract which means you have to make every method in that class in your program, whether you need to handle mouse holds or not. That can be annoying, but otherwise the programmer is totally in control of what the user can do. No cheating physics or "convenient errors" in your program.

In general, using a non-native language for realtime applications like games is a no-no. Still with 2 GHz computers common and 3 Ghz boxes becoming so, I guess that it doesn't matter as much as it used to.