There are a lot of unexpected surprises in this game. I just finished the main campaign. Honestly, this is apples and oranges to the likes of ACM or even AVP Classic/AVP 2. This is unlike any Alien game ever made so it's unfair to compare it to the predominantly first person shooter titles of yore. With that being said, this is one of the most faithful renderings of the Alien universe in video game form, and is by far the scariest and most intense one ever.
The DLC missions are both great fun and extremely challenging. As is Survivor mode. Again, this game has plenty of nuggets I never expected, but in a good way, not a "oh man I can't believe the did THAT" way. Cheers to CA for putting out a great game.
With that said, I wish I had a better system than PS3. Some glitchiness and framerate issues there.
Forgot to mention, by far my least favorite aspect of the game is the android combat, mainly because they're so damn DIFFICULT to kill, and also because I feel they are overused in the latter half of the game. Good thing you can adjust difficulty settings on the fly
I played about the first half of the game on Hard and then had to wimp out and bump it down.