I only watched this recently, and I really enjoyed it. Gave me a couple of good, sleep-deprived nights. Mainly because I watched it on the night shift when I was the only one here.
Though it didn't affect me as badly as
The Blair Witch Project. I didn't feel comfortable in basements for months after that.
I love a good horror movie, but most of what's been put out the last few years have been nothing more than gore-fests. While I don't mind those on occasion, I prefer the "less is more" type horror, which PA definitely falls into.
Now, granted, I'm coming at this as a person who loves to watch movies, in general, as opposed to someone who has been actually
making films for a while. Maybe my opinion will change once I've made a few shorts and have learned a thing or two.
On a related side-note, it's really refreshing to see the typically polarized view of this movie, but without the usual "If you liked/hated this, you're an idiot!" comments that you see on most forums.