A pretty solid shooter...but nothing more than that.
Prey looks great , but quite honestly Quake 4 probably made the best use of this game engine... and it runs pretty well too. Prey offers up some really cool ideas... LOTS of portals... in all sorts of places, playing around with the concept of gravity, upside-down walkways and a "spirit mode" ... these are all pretty cool ideas, but the problem with them is they don't really change the core gameplay at all.
The weapons are also "unique" , but that's basically because they look different. They can all actually be translated into "rife", "shotgun" , "grenade" and "rocket launcher " (which looks pretty damn cool though). And the game also features some brief vehicle bits, thankfully not too long, just about right.
But the problem with Prey is that it's really not outstanding on any level that really means anything. The actual level design is cool because of the additions listed above, but it's also horrible because most of it is in organic alien doorways which feel way too much like Doom 3's...difference is, Prey isn't meant to be a horror as such. The game is also really too easy and this takes the thrill out of it somewhat... it's also short, but that's rather a good thing... much longer would have been repetitive. Prey is not a bad game. But it's really something of a clone, so it's good to pass some time with, but if you want a deeper FPS experience, I'd have to point you in the direction of FEAR or Half Life 2.