Are you the type of movie buff that only or heavily prefers serious movies? I used to be the same way, only like sci-fi horror or something high quality like the shining, or exorcist, etc
But keep in mind that a lot of genres are like that: war movies aren't all that diverse, romance movies aren't either, zombie movies are all about death/ the way we approach death and fight against it - not that diverse, action movies are usually pretty low brow even thoug the diversity among plots is amazing.
If you dont like the slasher thing, just check out some of the more high quality flicks. Ps, among books, horror is extremely lacking of unique plots unless you read steven king. I just read several of HP lovecraft's stories one of the best horror authors around, and they all sound the same.
So, i dont think that any genre is better or worse just better in diff ways. Peace.