Just found out about this and decided to check here for ANN thread.  I can't believe this isn't more known.

I've personally used Cryengine before - the best real-time engine in my opinion.  Unreal Engine still remains king because of the gaming industry's personnel being so trained on it, but their engine is the UE killer if they can tip the scales.  They've got the funds and base to make a marketplace to rivel Steam.