I think the ending definitely ruins the film. For me it's much more like the John Carpenter style of 'horror' where it isn't actually scary, but has a lot of fun themes from the genre. Definitely not trying to actually scare you. Also definitely not one of the top films of the year, that's for sure.
But for a small indie film I think it did great at trying something different. A bit of a commentary on how the world of television holds no limits and people will do whatever they can to maintain their fame.
I found the film entertaining for the most part, largely due to the comedy but I was at the same quite enthusiastic about what would come given the name "late night with the devil" and it disappointed on that end.