I re-watched Angst yesterday to make sure I still wanted to include it on my list, and I wasn't quite as taken with it as I was when I first saw it a few years ago... Still, it's a striking film with an unsettling and off-kilter feel due not only to its central performance—Erwin Leder fully embraces the role of a murderous, narrating protagonist—but also (and especially) due to its floating camerawork.
As a slasher film, Angst might be the best I've seen; it certainly deserves a place alongside the much better known and appreciated Black Christmas (1974) and Texas Chainsaw Massacre (1974).
Here's what Gaspar Noé wrote about the film in the 2012 Sight & Sound poll:
"A great lesson in visual imagination but also in psychopathology. This film, still poorly known film in Anglo-Saxon countries, was my perpetual point of reference while shooting Seul Contre Tous. It’s the most emotional film about a murderer that I’ve ever seen. I had a VHS dubbed into French that I showed my friends about 50 times."
(Don't be discouraged from seeing Angst if you loathe I Stand Alone / Seul Contre Tous ; I do as well.)