Just got back from an early show, great film but I agree with Spyder on one point, the marketing for this movie is definitely all wrong. There's basically no real horror, at least in what most people consider horror, outside maybe a little at the end. Classic example of a Frankenstein-esque tale about raising questions about the darker aspects of the corners that science can touch in intelligent and unsettling ways. Excellent performances from the three leads, though admittedly some of the supporting cast was a little weak. I'm hearing a lot of negativity towards the climax and ending, which I can agree with; what happens makes sense in the continuity of the film and such, but felt somewhat inappropriate and could have been done much better. However, I won't say it ruins the movie, though it does bring it down some.
I can understand how some people would feel awkward or strange during certain scenes (Personally, I wasn't so unsettled, but I was with friends who were all basically wiggling in discomfort). I think people are mostly uncomfortable with the fact that something that shouldn't really be or act human in their eyes doing things that seem a little too human. I have no doubt that was the intention on the director's part though.
I won't be surprise to see this under perform, but I have faith that it'll build a strong reputation in larger years and be up for a rediscover with media release. Beware, this really isn't the kind of movie made for summer fun and entertainment, though, so if that's what you come in expecting, you'll probably be disappointed. Overall, I loved it though, will probably buy it once it hits DVD/Blu-ray