Orson Scott Card once said that dread is a much stronger, much more effective emotion than horror. The dread of anticipation, the suspense created by not knowing precisely what's out there, is much better than the shock value of pure gore and violence.
And that's why Disturbia was an excellent movie. It's the best execution of dread I've seen in a while. Unlike the typical horror movie, which nowadays consists of the main (unkillable) villain taking everyone out with a weapon of choice, one by one, in a fairly predictable fashion, this movie combined mystery, murder, and yes, romance (sorry, couldn't think of another 'M' word...).
The best parts are the parts right before something happens, when you know that something is going to go wrong, but you aren't quite sure what. You know the old man's hiding something, but how? The movie keeps you guessing in the most suspenseful manner. Then at the climax, most of the mystery gets revealed and the movie changes pace, slipping into a last-ditch attempt by the main character, Kael, to save his mom.
It was extremely well done. I particularly like how the killer did not have any supernatural elements associated with him. As much as I appreciate horror movies in which the supernatural plays a part, it's always a good change to have regular, human villains. That makes it much more diabolical.
So if you're thinking of going to see Disturbia, I do recommend it. There's some blood and a fair share of violence, but if you're looking for a gorefest, then you'll probably be disappointed. If you're looking for a good, suspenseful movie, go see it.