Not as good as the first one, but still worth seeing if you really liked the first movie.
This may be a little bit of a spoiler, but this is a prequel to the first Paranormal Activity. The people being haunted this time is a husband and wife with a teenage daughter and an infant son. The surprise is that the mom's sister is Katie Sloat, the victim from the first movie. By the end, they will transfer the demon to Katie, setting up the events of the first movie.
I thought the first movie did a much better job of ratcheting up the tension. This movie has too many sequences where nothing happens for the first half hour, then suddenly all hell breaks loose. The baby is levitating out of his crib much too early, and that almost made me laugh when I saw it.
I like a movie that does a good job of creating a sense of dread, but it's not that hard to make the audience jump. Just have a quiet scene, then suddenly a loud bang. That happens too often in this movie. Good job, you made me jump. Congratulations, scary movie.