You'll probably enjoy this more if you're open to cheeseball horror-comedy. It isn't a cheeseball horror-comedy - not quite - but it definitely plays better if you can roll into that mindset, and might have been a better movie if it were.
I sat through the first hour thinking this was a good premise marred by bad decisions. The dialogue is clunky, there are plot holes, Officer Cliché's unnecessary sideplot is a whole mess, characterization is all over the place, what are motivations anyway, etc.
But then that reveal hits, and I cackled with utter delight through the last 20 minutes. I would gladly watch the whole thing again with friends to watch them when that moment arrives, which makes it a good enough film for me despite the aforementioned flaws.