For the most part, film trailers are pretty similar. There's some expository dialog early on to get you oriented to what's happening, and from there they kind of take you through the highlights of the film: The major plot points, the best one-liners, the baddest-ass explosions or fight scenes. They're like frenetic mini-movies with more montages than regular movies. In that way, you kind of have to hand it to the trailer of Paranormal Activity 2 for going out on a limb. But when you go out on a limb, there's also the chance of falling out of the tree.
Actually, the general conceit here is pretty effective -- the filmmakers are clearly going for a Blair Witch, you-are-aware-of-the-camera thing, and their sense of timing is pretty on-point; the extended seconds of static before an object suddenly rushes toward the camera make that first scare genuinely effective. But right after that is when it gets weird.
Around 0.28, was that a film-watching audience we just cut to? Why yes, it appears it is. Scary things are happening in the movie inside the trailer, and and audience watching the movie in the trailer is reacting to the movie -- or is the audience part of the movie, too? Is that going to be in there? Who knows.
The thing is, while the trailer does an honest job of creating a creepy vibe, it offers almost no indication of what the movie will be like -- is there a plot of some sort? Characters? Or is it just going to be roughly 90 minutes of mood-lighting and stationary cameras? Then again, the movie is a sequel, so maybe the target demographic already knows what to expect.