Horrific, surprising, at times beautiful (and at times schlocky as hell), I was left physically shaken at the end. The geometry teacher, as has been mentioned before and often, was terrible but the central performances were all stellar.
Argento #3 for me. It looked absolutely beautiful (as all of his films so far have) and it was dripping in atmosphere. I feel like I want to watch it again immediately, even though it was the most straightforward of his films that I've seen so far.