[cheebacheeba]

You don't like Psycho on the grounds of how cheap it looked, yet didn't even give a movie with a pretty cool plot a go...though you like Paranormal Activity.
And you're asking for educated opinions?
Right.

Here's mine then.
If you're an adult, in order to enjoy a horror film - look for those high in tension or atmosphere, and/or those that have a human element so it's not so much the visual horror or killings and splatter that you're scared by, but the confrontation of something you find difficult or scary to deal with.
Also be willing to suspend disbelief if it's something more over the top.

I might suggest "The Mist" and "A Serbian Film" but those have more elements of sci-fi and thriller to them.
Event Horizon and Phantoms were a couple more of the supernatural/sci-fi type horrors that I've enjoyed.
Visually fucked up? Uzumaki.
Brutal? Haute Tension, Wrong Turn and Creep (that was quite atmospheric too)
I saw one called "The Ruins" lately that had a rather fucked up idea behind it.
Films like "The Signal" and "Carriers" I found interesting and chilling for different reasons.
Though really tastes are subjective, you might hate them and call me just another of the uneducated masses.