I don't like UEs especially UE3 which is for ungodly reasons a trend now. To name few reasons: UE games have notoriously bad mouse input, horribly optimized performance (very little gain from lowering graphics), capped refresh rate most of the time, UE games seem to be spawning like fish these days.. and what Shard said. Developers who work on lent engines (especially UDK) tend to be lazy, lacking of experience and abandon/give up type although I'm generalizing a lot here.
Unity.. Isn't that like game maker studio, but for 3D games?