I use it for some time now. There's nothing like it when it comes to ease of use.
I didn't know much Java script but was able to do some nice stuff after a short time.
But anyway, jscript is easy to grasp, there's lots of reference for it, everyone can code jscript.
Right now the webplayer only supports IE, but for the summer they scheduled firefox support aswell.
This is a great tool for kiosk systems or as a giveaway app on cd, cause you can export .exe files.
To me the obvious alternative to ShockWave3D is Unity3D, although the authoring environment is still Mac only, it can publish to Win exe and run as a web plugin. A Windows version of the Unity application is on the way but no release date yet. I don't mind though, as I bought a Mac Pro quite recently ( mainly because of Unity )