Impressive showcase. I have to idea how to tie a graphics rendering engine into a game engine, though. Sounds complicated.
It's not too bad because there are packages around for physics, collision,sound, etc, but it's quite a bit for one person. I've filed it under long term for my Ogre project. If you want to actually get something people can play in a reasonably short time, you need a complete engine. The other engine looked pretty good, but then it runs on Mac and not Windows so you're really in the same boat. I still haven't found a 3d engine that satisfies me. Ogre comes close enough, but it may take quite a while to get it to do what I'd like, or maybe the Blender plugin for Ogre will actually happen one of these days.