I hated Prey. The first hour was amazing (it was also the hour that was released in the demo.) After that, it was just one boring tunnel-room-tunnel map after another, filled with uninteresting enemies and a completely retarded "death" minigame that made you immortal.
I didn't even think the demo was great. It showed potential until the action started. Then you just got portals that were no longer exciting, a stupid minigame at death that just wasted time, and stupid soul jumping or whatever they called it.
And lots of anus doors.
I don't get why so many people go "ewww, UE3, everything looks wet!" This game was the very definition of everything looks wet. That should be a good enough reason for people to know it's less the engine and more the hands using it, but whatever.