I loved this film purely for the "monster". A good monster comes on slow, you catch wind of it long before you grasp its true nature, and by the time you get what's happening it's already too late to run. Every time we saw a new critter you learned something new, but you didn't really get to understand what's going on, if at all, until the end.

The rest is all window dressing in support of that, for me. Science Rambo and all, no bother. Just give me a steadily increasing apprehension of dread that never plateaus until all is lost.