As far as I am concerned, the ending of a movie has the ability to ruin the first 90 minutes.  I do not know if there is a better example of this than with Rest Stop.  The movie had sort of a cool feel to it until the end.  I found the end of this one so disappointing that the whole rest of the movie then seems worthless. 
It may just be that John Shiban's (writer, director) style is one that I do not get.  I have also seen Sublime and was not particularly interested in it either.
One positive note is that Mr. Shiban does seem very adept at developing extremely disturbing characters.  The religious family travelling in the RV is definitely creepy and ominous.  I also read that this worked really well in Otis, which he produced.