One of the best aspects of this movie (which is NOT, as it has been marketed, a horror movie) is the depiction of the internet into a physical space. It is really, really well done, and anyone (even slightly) familiar with the world of chatrooms will be blown away by the realism.
The movie goes back and forth between "real life" (the outside world) and internet life (the conversations and chats of the protagonists, here represented into a physical reality, so as not to spend an hour and 46 minutes filming youth typing on a keyboard).
It is not a horror movie, but rather a good psychological thriller, with the story of a disturbed teen who tries to alleviate his own misery by making others miserable. It is also a good look into the seedier, sleazier parts of the internet, where anything can happen, and where violence (although entirely psychological) can be very, very real.