I enjoyed this sequel more than American Paranormal Activity 2. The pace is much faster and the characters are more likeable. The movie is nicely connected to the other Activities and doesn't feel out of place. Still not a thrilling movie, but, in my opinion, none of the PA movies are. I liked the ending - whenever you think everything is over, you get something more. The movie does mirror the first PA a lot (some scenes are very similar), but still felt different enough and wasn't boring to watch.
I wouldn't call it a masterpiece of the horror genre, but comparing to the other Paranormal Activities this is one of the best.