Well I just finished chapter 1 (PS3 version) and I can say if the rest of the game remains this good, this is definitely among the best survival horrors out there. Some impressions below and I'm not going to bother with spoiler tags, so read at your own peril.
There's no installation required, mandatory or otherwise. It started with about 20 seconds of loading, then you watch the cutscene and a very smooth transition into game play. There's no loading within the game except in between chapters. Although you can say the elevators rides are the loading part, just like Mass Effect (though not as long).
It take a while getting used to the 3rd person view with the character standing a bit to the left, and the pop up menu that moves with your right stick. The 3d map is confusing and kinda useless, but one thing I like about the game is if you press the R3 button anytime during the game, it shows you a path to your next mission objective.
The gun play is pretty much like a standard 3rd person shooter, and there's not much to fault here. The atmosphere is where the game shines. The smart use of sound effects, shadow and lightning makes sure you always have to look around corner and at your back at all times. So far, the game gives me a very strong Alien vibe, both in terms of environment and plot. Though I must say the voice acting and script, while acceptable, ruins the atmosphere a little bit. I wish the 2 crew members would just shut up already.
The only problem I have with the game right now is once I switched to the DLC scorpion suit (given for free in my version of the game), I can't switch back to the old one. Hopefully I can do that in later chapters of the game.