Paranormal Activity review

After watching Paranormal Activity, I had a very difficult time determining if this was the scariest movie I had ever seen. Surely it could not be. This movie? With its $11,000 budget? With its total lack of gore? With its cast that could be counted on one hand? (Note: there are no spoilers in this review)
I have yet to answer this question, but that isn't important. What matters is that it sent shivers down my spine for several minutes after I had watched it, and it made me realize that no film has ever inspired any real fear in me. So obviously I enjoyed this film, but let's see if we can't apprehend a few of the reasons it worked so well.