One of the worst things you can accuse a scary movie of being is anticlimactic. If the whole point is to get people to feel something - fear, anxiety, horror, unease, whatever - then not paying that off is a problem. Even if you're doing a great job scaring/freaking out people along the way, you sort of create an expectation that it's all going to culminate in something even scarier/freakier. I think most people agree on that, but trying too hard is a problem too. You have to know when to let the story breathe, when to let the weight of what's happened settle in, there needs to be quiet.
The Crazies has a good story to tell, but it doesn't know when to shut up.
Ogden Marsh, Iowa is an all-American small town, and they're getting ready for an annual festival. The town sheriff is married to the town doctor, there's a high school baseball game going on, the sun is shining, and you just know a picnic is going to break out at any second. In the middle of this bucolic charm, a lone figure walks across the baseball field, carrying a shotgun. It's the town drunk, looking oddly blank, and his refusal to put down the gun gets him shot like a dog, Needless to say, this casts a bit of a pall over the festivities. In its wake, the people of Ogden Marsh begin acting strangely, and people begin dying. The sheriff is trying to outrace the disaster, but even to the extent he's successful, it's all too late.
Normally, a small-town-goes-crazy story builds slow and ends with the entire destruction of the town, but we cover that much just in the first act. The rest of the movie is really about what happened, why, and what kind of efforts go into keeping it from happening again. And this is where the problems come in. It's great that the story doesn't take the turns we expect it to take when we expect it to take them, but it also doesn't know when to quit. It keeps adding one more problem, one more twist, one more escalation, until it ends up in the realm of the ridiculous, from what started off as a pretty down-to-earth, plausible story.
Ultimately, this means that the parts that are especially effective get buried under the sheer volume of stuff happening, like someone has something interesting to tell you, but it's stuck in the middle of much less interesting stuff, and the person saying it keeps getting louder, and louder, and louder, until any worthwhile information is drowned out by inanities shrieked at the top of the lungs. What should have just been a quiet story about the death of a town ends up a conflagration, everything we cared about burned away without much consideration for what was good about it to start.
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