The best Single player game to day. Raises the bar, but as with all good fps games, a little short.
The start of the game is rather clever. Your are looking at a mirror. Funny thing is, you will be walking through very similar objects and trickery in a few moments. Then after the special-effect saturated pub start as featured on the demo, you see Tommys environment change to the organic setting that continues throughout.
As for the rest of the game, it unfolds in a neat little package, not like something like Farenheit, more like a simpler doom 3 storyline. All there, with little confusion. The gameplay has revolutionary puzzles, which make the toddler-minded HL2's seem sub-humanly simple. They are not overly complicated, but they can easilly confuse you at first. The puzzles can also use the physics system in a not so cheesy way as used on previous games with similar engines. It all adds up to some very confusing and clever gameplay.
The music is another thing I need to mention. It easilly makes this as good as a movie, especially at the later seens with the "changed" Jen, and the major fighting afterwards. It helps add some decent emotion not seen in many other games, from the loss, to anger in one song.
The only slight flaw that prey has, is the length of time it takes to complete. I did it in 6 hours, with breaks in that, so wethin 5 hours, you will have saved the world. Unlikely, but then again, thats the way all great games seem to be going nowerdays, like Cod2, HL2, FarCry etc. What ever happened to the days when it took days to finish??? Ah well...
As for the graphics, since it runs on the Doom 3 engine, you know its reliable, and damn good lookin'.
As a final sentence, this game is really really good fun.