I think it was a big mistake...
...to kill of certain characters so early, especially Tony the Pimp. Actually, he should've been one of the survivors.
The movie sets up certain characters at the beginning and some of them get killed mere seconds into the whole outbreak (like that bastard husband, I forgot his name, imagine if he lived and treated others like scum, the interactions between him and Tony would've been priceless).
Imo, for me the movie loses some steam near the end because of that, it becomes kind of boring because Cheryl and George aren't so interesting and they're the only ones left.
It becomes clear the writers wrote themselves into a corner and weren't sure what to do when it comes to some scenes.
Don't get me wrong, I like this movie, but it could've been so much better with some changes to the script: characters staying alive for some more time, characters working together more and trying out various tricks to fight and destroy the demons.
Hell, the masked guy should've been present in the cinema as well, acting like the leader of the demons.