I watched Paranormal Activity on its opening night. Simply put, all of the comparisons to The Blair Witch Project are wholly justified. (Apropos of nothing, it's the first film I've seen in a theater since Penelope was born. There's no particular reason why this film was the first - it just worked out that way.)
The way that PA starts with subtle scares - creaks, lights turning on, gently moving doors - and gradually escalates - bangs, spontaneous combustion, slamming doors - is damned effective. By the time the sheets on the bed begin to move we're scared in part because, well, the scene is scary but moreso because we're already anticipating its escalation to... well, it's one thing to spoil the plot and another thing entirely to ruin one of the most terrifying scenes I've ever seen.
If PA improves on the BW model in any respect, it's with its rather rigid structure. It moves back and forth between what the stationary camera in the bedroom records in black-and-white at night and the characters' discussion of what's happening and what they should do about it in color during the day. And those breaks - knowing that the characters, and we, are safe when it's light out (that is, until the film nears the end, when even the day is no longer off-limits) - keeps us from feeling exhausted and keeps the film's scares from seeming arbitrary or, worse, dictated by the cliché structure of a genre exercise rather than the internal logic of the story.
And they also make the nights that much more frightening, the anticipation that much stronger, and the pay off feel that much better because it's deserved. I noticed that the audience would nervously, and collectively, shift in their seats as we transitioned to the stationary night cam near the beginning of the movie. By the end, people were gasping simply because the title for "Night 23" appeared on the screen and the picture faded to black. You know they're doing something right when we're scared by the expectation of being scared but still haven't any clue how it's going to happen. (As opposed a scene in a typical horror film where the scare is practically choreographed for us: If the perspective is over the hero's shoulder and a few feet behind, is there any way that it won't end with someone grabbing him/her from the back?)
But I didn't particularly like the last 20 seconds or so of the film. In Blair Witch, the ending is ambiguous but powerfully suggestive, harking back to one of the myths that we heard in the first 1o minutes and leaving us with little concrete evidence of the characters' fates even as it leaves us with a strong sense that we know what happened to them. (Even if we don't exactly know how it happened.)
Paranormal Activity missteps, though, and it starts with the day preceding the final night. It's implied that Katie might be possessed by the demon that's been haunting them, but this comes entirely out of nowhere. (She had been sleepwalking earlier in the film, yes, but that episode made seem fearful, not sinister.) When night falls, the scene unfolds incredibly alike the finale in Blair Witch - off screen screams, a character racing downstairs, a commotion in the dark, and silence. When we hear footsteps climbing up, it's not certain that things have gone wrong. And then Micah's body flies at the camera - which is terrifying, but wholly inconsistent with the more mundane scares that we've seen to this point. And if that weren't enough, the possessed Katie, who has presumably thrown Micah at the camera, shuffles into the room after him, bending over his body, and then roaring at the camera and breaking it. Roaring with a computer-enhanced demon-face. That's right. A movie that began by exploiting our all too real fears that creaking doors might not "just" be creaking doors resorts to bad CG and a demon-face. What. The. Fuck.
While I was writing this, I checked Wikipedia because I remembered hearing that there were alternate endings. And there are two, apparently: one in which only Katie returns from the ground floor, and she sits on the floor beside the bed; another in which, again, we only see Katie and enters the room only to slit her throat in front of the camera. I would have preferred either one. And then I read this on the same page: "The ending currently attached to the release of the film was suggested by Steven Spielberg." Spielberg, incidentally, wanted to remake this film and had to be convinced that this was far scarier than anything they could do with a bloated budget. Why am I not surprised that his one (ostensibly) contribution is the very worst of the bunch?
(And while no one asked, I would've gone with an ending quite unlike any of the three they made. I wouldn't have had Katie return from the ground floor at all - it would have been Micah. And if anyone cares to ask, I can try to explain what and why in the comments.)