R-rated horror movies that waste their rating are almost as disappointing as PG-13 horror movies.

How did it waste the rating? Did you want more gore or something? I think that kind of thing can hit overkill too fast. The best terror is achieved by judiciously doling it out. Show less, imply more. Jaws gets a booster shot of horror from shark's absence. It makes it more menacing. When you can't see it, it could be anywhere. Same principal at play here: if you show me limbs floating around, it's gross. If you show a gator come from nowhere and drag a dude into the water, I assume there was dismemberment and I fear what comes next for characters I care more about.