Insidious is a tautly-crafted, old-school, genuinely terrifying movie.
Some of the crappier reviews of Insidious throw around the word "cliche" but don't you believe it. Don't believe the inept and condescending critics who say things like "you'll like it if you've never seen a horror movie before." Genre is wasted on these dorks, who prissily sit there and tick off the things they recognize from other movies. Yes, the film references other movies in a fan-boy kind of way. Deal with it.
As for those who complain the scares are lame, well -- ! The much-derided baby-monitor scene spooked the hell out of me. I don't know, I guess I find simple things like demon voices on baby monitors frightening. I'm a simple woman, I guess. But the scene I really, really, REALLY loved more than anything else in the movie was the one in which the weird midget guy starts playing "Tiptoe through the Tulips" on the record player while Renai (Rose Byrne) is outside putting out the garbage. I love the way it's shot, with her hearing the record before glimpsing him through the window. I love the use of sound in both these scenes. (One critic said the film relied too much on sound. Say what?) And what about the scary old lady in the photos, getting closer in each picture? How on earth can anyone not find these concepts, these images, scary as hell? And don't say it's because you've seen a lot of scary movies before. If a 19th century newsie ghost started fucking around with your record player, you wouldn't act so cool.
Things do break down a little in the third act, I will concede that. I can see the necessity of the father fighting for his son, I liked the romp through the haunted house, I even liked the twist. (Again, as with the whole genre-versus-cliché argument, there's something satisfying about a twist that you see coming.) And oh how I loved all the ghosts crowding into the house. I don't know that I would have given up that pleasure, even though I sort of wish the story had diverged after the seance scene. (How I would have done it? Let the demon posses the boy, kill the boy. Maybe I would not have gotten a PG rating.) The break-down, as I see it, only stems from the necessity of tying up the story. In other words, there's less of that amorphous creepiness I so enjoy, and more plot strands dutifully tied up. It doesn't feel like a climax so much as a chore duly executed.
Luckily for me, the rest of the film more than makes up for the imperfect third act. The true genre pleasures are all present and to those who decry them as clichés, I have to ask them: "How would you have done it? What totally original spin on the concept of haunting would you have come up with?" Or, more theoretically, "Does it make you happier to deny yourself the pleasures of genre than to immerse yourself in them?" Likely I would be greeted with silence. But not an ominous silence because, you know, that's totally been done before.
