Saw it, and liked it a lot. It's not very often that I see a movie that can make me jump, but this one had a couple of good spookers in it.
The effects are well done, and a lot of the gore you might expect is implied instead of being on-screen. I personally like it better that way. Let the audience imagine it as bad as they want instead of telling them how bad you think it should be.
The story is actually not too bad for a horror flick. The premise of high school age kids being killed off one by one is certainly nothing new, but the way they find themselves in that deadly situation is.
Bottom line, I thought it was well worth the full price of two tickets. If you don't like getting scared then you should probably go for the matinee, or maybe even wait for the video.
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Never underestimate the power of stupid people in large numbers.