I thoroughly enjoyed. Once I realized what the film is really about, which was fairly early on as Whedon really doesn't hold back and the plot developes gradually rather then with a sudden twist, actually found it somewhat predictable. However, its originality is still praise worthy, the wit is sharp (which is very important since there is alot of it), the homages are constant and appropriate without getting in the way, there are a few good scares, and the gore is great- reserved for much of the movie and then over the top when the times comes. On the negative side, the CGI, which is on full display for the climax, is rather poor and the very end is somewhat unfulfilling.
IMHO, this and Tucker and Dale are the best horror comedies of at least the l past decade.