I watched Paranormal Activity 3 the other day. It was alright, not too scary, just a tiny bit creepy and in-explainable. I really liked the camera capture style that they used, though kind of predictable.
I had a hunch it was possessing the bear at first.
Anyway, 3/5 stars for me. I haven't seen the first 2, but I know it has some connection to the first two.