It looks like a Doom 3 mod, b/c it basically is, its designed on the Doom 3 engine but they did not do as good of a job. I have In fact played it, and it is fun. I had a better time on it them on Doom 3 even though it did not look as good. Its still fun, great game, just don't expect any revolutionary game play.
id Software bascially used the Doom 3 engine for Quake 4. It's a pretty good engine. It doesn't hog up lots of resources unlike some...other...ones...*Cough* EA *Cough* The only thing I don't like about the Doom 3 engine is that it looks fake. Too glossy and bump-mapped.