Okay, so I've had some time to think about it.
It took me a long time to get into it, and I don't know if it was because they didn't set it up well, or if it was because I already knew the premise (a little of both, I think). The red creatures threw me off, because the book I read didn't have such things (all it has was the adults telling the children they couldn't go in the woods, but all the kids were younger, and the premise was that they lived in a Colonial House/Truman Show-type environment, where people would come and watch them live without the kids knowing what was up).
So I was still freaked out by the red things, and I can't BELIEVE they didn't do anything about the psychotic killer in their midst. They kind of just hoped it would go away, it seemed, but sheesh, isn't this what they were trying to prevent? Obviously their little experiment didn't work. There will be crime anywhere there is civilization, whether you take your culture back 100 years or not, because where there are people, there are people who will do bad things no matter what!
So what I don't understand is why, when they realized they had a psychotic killer among them, they weren't able to say, "You know what? This isn't working! People are the same everywhere!" instead of continuing with a farce, lying to their children and scaring them to death of creatures that didn't exist, in the name of so-called safety.
I liked Ivy and what's-his-name, River Phoenix, though. They're strong characters, and I liked that it was Ivy who was the one who made the run through the woods--not only is she female, but blind on top of it. And she still kicks butt!
Okay, similarities to the book:
It's been a few months since I've read it, so it's all on recall, but pretty much it's *exactly* the same plot. Main characters are older, so Ivy has a love interest, and she's blind. But it's basically an isolationist community, and the girl protagonist has to make a run through the woods to the nearby city to get medicine for someone in the village who's sick. In the book, there's a cholera epidemic that she's trying to prevent any more children dying of. It's not really clear in the movie what the first child died of, but I thought it was cholera because of the book. When no other children died, I had to change my mind.
I think what's happened here is that the studio liked the basic idea of the book (they had optioned it, you see), but didn't want to have to stay true to the book. So they've used the basic plot, the skeleton, and given it new flesh. That can make it very hard to win a copyright suit, because I think the rule is that you can't copyright a plot, just specific details. It'll be a tough case to prove, I think, but I also think Margaret Peterson Haddix is justified in thinking that they've lifted her idea.