I've never really liked horror films, but I think some of the recent trends in the genre have represented multiple low points.
Everything Rob Zombie has directed would be one of them. His films are inane, empty, amateurish derivative crap.
There's also the trend now toward shock/gross-out/torture horror films like Hostel or Saw which really don't have much at all to offer over the average snuff film. Final Destination might also fall into this category, though that borrows elements from the Scream/I Know What You Did Last Summer "smart/hip teen horror film" subgenre as well.
That trend (the smart/self-aware teen-skewed horror films) I didn't mind so much. But after the first Scream, the level of cleverness went downhill and eventually this subgenre was just as derivative and unoriginal as the classic slasher genre it was lampooning.
The trend of copying Japanese and Hong Kong horror films I also find pretty dull. The Grudge and The Ring fall into this category. The redone Exorcist might as well. Similar to the shock films, they offer a few creep-out thrills in the form of "creepy" visuals- like pale girls with matted hair or little Japanese boys screaming like cats- and not a whole lot else.
The horror films that I like are those that have substance beyond the cheap scare/thrill/gross-out/creep-out. Films that either have some kind of interesting story behind them, or are directed by people who understand what it means to build up suspense and make a film psychologically unnerving without resorting to the cheap carnival side show cop-out shit I listed above. Films that really have something to offer in terms of great character performances or inventive visual or narrative styles I can also appreciate. Basically.... if the movie can stand on its own even without being "scary"... because movies don't scare me... then I'll probably like it.
Examples of the above would be Alien/Aliens, The Shining, Sleepy Hollow, The Terminator/T2, Fire in the Sky, Jurassic Park, The Sixth Sense, Akira, Scream, Jaws, 28 Days Later.
Many of those could be filed under multiple genres, but I think almost all of the best "horror" films can be.