Something I decided to do for fun. My previous list, which reached over 300 titles, has been archived. As far as what constitutes horror, YMMV; much as I love everything in the top ten, it'd be easy to force three or more of them off just by letting in, say, F.W. Murnau's Faust, Elem Climov's Come and See, Michael Tolkin's The Rapture, and Jean-Luc Godard's Weekend (and that's just getting started).
Nominees (that is, films I've seen for the first time, and will consider for a period of at least six months, with at least one additional viewing required before making any calls):
*Deathdream, aka Dead of Night (1974), watched 5/30/2016
*The Neon Demon (2016), watched 6/27/16
*The Act of Seeing With One's Own Eyes (1971), watched 7/12/16