Personally I think it's a different type of horror, verging on 'psychological thriller' like Rog was saying. But for argument's sake, as far as scary goes I'd say Japanese wins hands down. You're totally right though - I can't remember what the last American 'horror' film that freaked me out was.
Something else I think is vital and missing most of the time is character development... or even interesting characters (usually the villain/killer/horrible thing is fucking cool, but besides that you're got the body bag fillers and the lifeguard hero or lucky screaming girl that survives; they're cut-out and empty). In most Japanese horror movies a lot of the film is spent establishing the viewer's relationship with the main characters, and showing how they are regular, normal people
like you. It's kind of a cheap trick, and I'm surprised it hasn't been exploited to death, but if you have an emotional attachment to the characters, what happens to them is going to affect you much more.
AUDITION SPOLIER
If you went into this movie blindly - I saw this film without even seeing the package... knew nothing about it - you were in for a pretty big shock. For more than half the movie it's like an almost comedic romantic tale. This light hearted nature just makes the turn of events that much more powerful.
Deeper deeper deeper deeper deeper
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