Java can use DirectX, OpenGL and Java3d (which use Direct3d or OpenGL, as you wish). So using 3d hardware acceleration, Java would be fast, not as fast as C++, but java+opengl is available for almost any OS/platform, so you''re game/app could be played/used by much more people and you''ve only one version af the code to work in.
I think it''s something very interesting. Another thing is that the fatest most beautiful 3D game, aren''t the best games...
-* Sounds, music and story makes the difference between good and great games *-
There is actually a discussion going on in the Java 3D listserv group about develping a paticle system in Java 3D. According to the posts they have made some progress.
Your point about the quality of graphics versus the quality of the game is well taken. For instance, one of the best games I have played to date is Alpha Centauri. There is nothing spectacular about the graphics or special affects in the game. Gamelan has some article about attempts to build an Alpha Centauri-like game in Java.