First of all, I just want to say that the movie has, most probably, the best score I've ever heard. From start to finish, it is almost as if little tension is always building in your stomach. Conveniently, the score works perfectly with the isolated, awkward mood of the movie. Secondly, there were moments when I felt like some shots were too long and there was too much silence, just enough to make me doze off, but when the movie was done, I noticed that I had a lot of questions. But most of those questions were about how I 'felt' about the movie. It was discomforting, but mostly cold and isolated...almost as if I'm watching Scarlett Johannson become human for the first time. She stalks men as if they were a social experiment...and not a sexual experience. I remember thinking, in the restaurant scene, that she's going to enjoy the cake--but she retches instead. We go from being scared of her (for her inhumane traits) to being empathetic towards her (that is, being in the shoes of a beautiful woman in the real world). You realize from her stale character that she's not at all human...and that seduction is seemingly her supernatural ability (and all she knows). However, as the story continues, it's as if she's slowly transforming from a robot/alien into an actual human. Moreover, I feel like this is one of the most realistic and logical portrayals of an 'alien'.
The motorcyclist's role still confused me and felt inconsistent, but the most outstanding role (other than Scarlett's) was the guy with face tumors. When Scarlett sees her reflection in the mirror, its almost as if she realizes that she isn't so widely different from him--as they both appeared human. Human empathy is one of the strongest themes in this movie. But also, the isolative elements (the play on the word 'alien') does bring some interesting commentary on Scarlett's role. She could be interpreted as a lot of things (especially what she represents in her role), but I would definitely recommend this movie for that sole reason: Scarlett portrays something familiar in our society as opposed to 'foreign/alien'