I haven’t seen many horror films, but the ones that I have seen have been pretty good to great. Here is a list of what the IMDb says are horror films I’ve seen and what I give them out of ten:
The Evil Dead (1981) - 8/10
Evil Dead II (1987) - 9/10
A Nightmare on Elm Street (1984) - 7/10
The Shining (1980) - 9/10
The Cabin in the Woods (2012) - 8/10
Drag Me to Hell (2009) - 8/10
Evil Dead (2013) - 6/10
Alien (1979) - 9/10
So yeah, I wholeheartedly disagree with you on your "Halloween is the only horror film that is well made" statement