I completely agree with those who think the last 30 minutes aren't on par with the rest of the film. Less is always more when it comes to the supernatural. But Wan isn't the first director to cave to audience expectations in the final reels.
If you're thinking about seeing this, you really should. The first hour or so is tremendously well done. And there are some legitimately great shock scenes along the way. I've seen too many horror films to get really frightened. But Insidious was creepy enough to get under my skin. Several images have really stuck with me--especially the figure at the window.