I'm ashamed to admit it, but I'm playing it on easy. I have no idea how much more difficult the higher settings are, but easy hasn't been easy at all. The Alien is very responsive and last time I played (I'm guessing I'm in the 2nd half of the game), it walked past me a few times while I was hiding under a table and to my horror, the 3rd time, it suddenly turned and killed me instantly without even a hint it was aware of me being there. Scared the bejesus out of me. This, after I've avoided the Alien many many times while hiding underneath a table. Turns out the Alien will in fact adapt to how you play the game. I have no idea if the Alien is even more aggressive on the higher settings - but even on easy, I am amazed to see how much you can agitate the thing. Shoot it or provoke it and it will result in the Alien coming down more often and running around as it looks for you.
On the upside, I have a full stash of everything most of the time; Over supply of med kits and other accessories that I never really need much. Not sure if this is something that is easier on the easy levels, but then again, I am playing it a bit like a chicken anyway - mostly crawling, hiding, crawling, hiding - and repeat. So I guess I'm pretty safe most of the time.
I will definately replay this again on a higher difficulty setting once I completed it. It's too good of a game not to.