First of all let me start by saying that this is a B-movie. Once you have that in your mind, and you appreciate that it is also a teen flick, you know what you are in for.
I thought the story line was OK, and yes the acting of the cops could have been better, but overall, I enjoyed the film. It even made me jump, (OK only once but that's not the point). Some of the reviewers here have slated this film, but maybe they thought they were going to be watching a big budget 'Hollywood' movie with huge amounts of CGI etc. The effects are fitting for the film. I don't think it needed anymore.
Yes, there are the odd moments when you can see a member of the crew trying to hide, but that can be said of a lot of films. If you are 'in the moment' you don't see them.
I would say that if you are looking for a film to frighten the pants off you, this is not it. It is still an enjoyable film, that (oddly enough) the teens will find great. 6 out of 10 for its genre.