I guess it's better than fucking poltergeist, but that's not saying much.
I haven't seen the two movies it's a prequel to, so I may not be the one to appreciate it, but even for a horror movie the plotline is just dumb. there are loooong stretches where nothing happens.
1. "parts 1 and 2 were much better" In response to Reply # 0
I'm pretty sure this was made for a couple of reasons:
-They wanted to keep making installments of this (SEE: Saw, Paranormal Activity), but without James Wan they didn't want to continue the story, so they did some backtracking, giving us backstory that really doesn't add any extra clarity, depth or significance to the events in parts 1 and 2.
-They presumed (a mistake IMO) that with Insidious 1 and 2 Lin Shaye had already reached Zelda Rubinstein status and, along with her two "Ghostfacers" supporting characters, could carry the movie. While they were definitely the most amusing people on the screen, they definitely weren't enough.
It wasn't terrible, but it took a pretty noticeable dip in quality compared to the first two movies. And it wasn't really scary at all. Although he's supposedly doing The Conjuring 2 first, let's hope Wan comes back for the inevitable Insidious Chapter 4...