I loved this movie.
A lot of modern action movies focus on just having fun lines and cool action scenes, but when you actually start thinking about the plot everything falls apart.
And well, I have certainly enjoyed movies like that (Hell, I watched Venom twice, to my shame), but this movie actually managed to do both. Be a fun popcorn fic with good one liners and have a plot. Foreshadowing, character growth, and flawed protagonists.
This is a movie I would definitely watch again, and I would put it with the likes of Shawn of the Dead and What We do in the Shadows, as one of the best horror comedies I have seen.
I don't know why it flopped, but sometimes good movies do, and critics never like comedies or horror. Don't let that prevent you from watching this movie.