A mess of slapped together parodies. They tried to shoehorn too many film references and it just doesn't quite work. If they had just stuck with the Paranormal Activity and Mama story lines, they might have been able to pull off a decent movie. The Black Swan, The Rise Of The Planet Of The Apes, and Fifty Shades Of Grey scenes just didn't flow with the rest of the parodies. I know it's supposed to be dumb, but it can still have a coherent narrative. Instead, this movie gives you a bunch of random parodies and crude jokes duct-taped together to make a crappy comedy.
Most of the jokes seem like they were the first thought that came to the writers. I'll improvise a Scary Movie 5 scene right now off the top of my head: "A guy tries to open a kitchen drawer but it's stuck, so the guy braces his leg against the counter and finally the drawer comes out and hits the guy in the nuts really hard. The guy lays on the floor in agony and finally sits up, only to hit his head on the drawer." This is what a typical scene in Scary Movie 5 is like. It's a bunch of jokes that haven't been thought out.
It does have it's moments, but for the most part Scary Movie 5 comes off as just a half-hearted attempt at humor. If they concentrate more on poking fun at the movies they are parodying and less on the lowest of low brow jokes, they might actually be able to keep this franchise popular. They also need to stick to parodies of movies they've actually SEEN and not just saw the trailer [which is what they did for The Evil Dead remake]. I've seen much worse parody films, but this one still isn't very good.