Yep, the ending ruins it (no spoilers)
They fucked up at the end. Until then it was a fun zombie-like horror movie requiring the usual amounts of suspension of disbelief for the genre. Damn, who thought that this ending makes sense? It is not even fun. It is just lame. I can't believe that this is same S. Craig Zahler who gave us 3 good movies. Granted, he wrote this one when he was 22 or something, but he had enough time to mature the idea.
I was going to give it a 7 until the last 10 minutes, but now it is more like 6. Still worth a watch for horror fans.