It's funny that you mentioned Unreal Tournament, because i think it's using one of the best fps engine there ever has been. It feels so good it was, and still is stunning. I had never before seen a truly 3-dimensional world built from round shapes and incredible collision and physics. To put it in perspective, many many commercial fps games have tried to be good. Almost every single one fails to get to level of Unreal engine. Lucas arts (All starwars based games), Quake, Half life, Battlefield... i could name a few more fps style games with inferior graphics and/or gameplay

Just want to be realist... You could make many good games in time this would take, if it at all possible.