What's great about this movie is the performances by the leads, Lundgren and FBI Agent Pierce (Kristina Klebe). They work really well together, when the movie isn't trying to push them toward each other. Those moments come off forced, with Pierce going from stick in the mud to potential love interest.
It's slightly balanced with Woodley being consistent. He's a fun guy to watch, and he's set apart a bit from most heroes, even if it's in ways that don't amount to much. It's mainly in the vape, the net gun, and the cowboy hat. It's the little touches that draw people to him. Strip those away and he's the smartest guy in the room, with a solid moral compass. It all adds up to a great savior that could show Evil Dead's Ash a thing or two.
The writing has a similar approach. For one thing, this is the only movie or show that actually does the police jurisdiction cliché in a way that isn't stupid. The FBI actually justify their reason for showing up, and it's something other screenwriters should take note of. Don't Kill It also builds itself up well, and quickly, making good use of its short runtime by focusing on the demon hunt and Woodley's character. At least that's how it seems on paper.
Mendez also edited the film, and at times it's choppy. It's most noticeable when Pierce is going over her origin. Every line is a separate cut, and every single one feels like it was shot separately from the one before it, so the scene artificially drags on. The action has similar issues.
The action just feels slow, like it wasn't well choreographed or edited. Impacts don't really connect unless they're gunshots, and the saving grace is that the movie was clearly done practically and on-location. People with a bloodlust are going to have to look elsewhere, but people into mild psychological torture may enjoy the demon reveling in its inability to die.
Don't Kill It is a fun action movie for all the wrong reasons, but that shouldn't stop it from being checked out.