I actually preferred this one to 4 and maybe even 3. Some terrible 1990 hiphop during the montages though.
Mario Bava's influential giallo and proto-slasher. Almost all of the tropes of the more grimey 70's and 80's slasher boom are there; from the young group of people having a sexy time away to the POV stalking, gory kills and lurid nudity.
Not my favorite Bava on an aesthetic level, but entertaining enough and ahead of its time.