This movie is a total attack on your senses. In a way, it kind of reminded me of the first 15 minutes of Irreversible, except I didn't hate it. First and foremost, I have to talk about the score. This is equally my biggest positive and biggest negative. The score is absolutely amazing. "Goblin" made one hell of a haunting, creepy score, and I loved all of it. However, it's blasted so offensively loud at you that it makes you wonder if "subtlety" is in Dario Argento's dictionary (it isn't). Good thing it was so great, otherwise I would have hated this film just for that. (And part of my loves the fact that what sounds like a whispered "rar rar rar rar" is a part of the main theme of this horror movie. It's almost too cheesy that it's awesome.)
Next up is the color. I think that's what this movie is most famous for. The use of color in this movie is outstanding. It's mostly reds, but there are a lot of blues and even some greens throughout. It gives it this ethereal quality, which only helps some of the later scenes. In particular, there's this round office when she's following footsteps and hunting for a hidden room. The way the camera pans around the office is almost dizzyingly surreal, like the room is just changing around her, though it isn't.
Unfortunately, the rest was a little rough for me. The story was very interesting, and it was definitely a slow burn. But I felt the production values were otherwise a little on the poor side. The acting was pretty bad (though Jessica Harper was definitely the best--and the cutest... totally unrelated). And because it was a slow burn, it sometimes had trouble keeping my full attention (when the music wasn't blaring me out of my seat). I can't necessarily even say it was the direction, as Dario Argento was responsible for making it as stylishly great as it was. So I don't know.
Perhaps it was an expectations thing--due to it being Argento, I was expecting more blood and gore, and possibly a little more body horror. But the film is surprisingly lacking in blood. I mean, it's there, but not much. There were some great set pieces, like the wire room (was that supposed to be barbed wire or just regular wire?).
Anyway, the film was a bit of a contradiction for me. It's like everything I really liked about it was also everything I disliked about it. The score was great, but it was too loud. The style was fantastic, but part of it seemed off at the same time. The acting poor, but fitting once you realize these were originally supposed to be 12-year-olds (and still made to act like children despite the older ages). The slow burn worked, but was sometimes a little wandering. I don't know... it was one strange little film, but in the end, I liked it.

I Am McLovin!