Bottom line, anyone else her familiar with either Plane Shift or Crystal Space 3d in general?
I have just started working on the CrystalSpace/CEL/Crystal Core project. They are working on some major engine overhauls and are pushing forward CrystalCore as a capability demo and working example.
CrystalSpace is a very good engine, powerful and flexible, especially once the current round of enhancements gets added. There is a lot of control for the level designer over shading and lighting. The project manager, for instance, just added the ability to control how doorways effect lighting of adjacent sectors. I would not say it is easy to learn, even for an experienced programmer. There is a good deal of learning curve to start figuring out how it is organized and how to make use of all those abilities. RIght now, it is fast moving and the stable (non-CVS) release is a little old.
There is quite a lot of example code, though, and a very active/helpful community.