A hard film to review, overall.
First, as I have mentioned before in a few of my 1100+ reviews, most film-makers secretly yearn for the "trifecta" of movie making -- which is low budget, small cast, single location. Since film (like everything else in our society, and I mean LITERALLY everything) is a business, even a moderate audience for such a low-budget film means profits, which means you are a hot ticket, which means you get new money for more product. Which means you have a new career.
So in this light Schneider (and I am a fan of his TV work) did the smart thing all the way. He not only went after the Holy Grail of film making (as above) but did so with a sharp concept (name horror stars hoisted on their own petard) with many of the cast playing against type. Clever. Very clever.
So what went wrong? Not much really. The problem is that, with such careful and meticulous preparation, this film can never aspire to be more than it was originally designed to be.
In other words, you have (perhaps) an instant "cult" film, designed to appeal to a youngish demographic that "gets" films that deconstruct themselves, and are looking to fill some two hours with harmless and forgettable fun.
On the other hand, this is not a true horror film (like Conjuring) not a true comedy (like the films Leslie Mann appears in) and is at best a super-lite version of the "ensemble films" that the late Robert Altman was known for.
Not bad for a first effort. But you are not going to see it mentioned at the Oscars.