I saw it this weekend and I *loved* it. It was so much fun. Great funny dialogue, very creative way of doing a horror film.
I do agree that it is derivitive of Buffy/Angel, but I consider that a good thing. The juxtaposition of funny dialogue, clever situations, and not-quite-scary "horror" is very Buffy-esque. I consider that a good thing and I'll take that over generic slasher horror any day of the week. Someone pointed out to me that...
I also agree with the comment above that it doesn't matter so much since most of the moviegoing public isn't THAT familiar with Buffy/Angel except in a casual manner.
I also feel tonally the movie compares favorably with movies like Men in Black, Zombieland, and Scream.