I’m really not the best audience for this homage/parody/innovation/post-modern-reflection of the horror genre: I don’t know the genre well, and I’m ambivalent on Joss Whedon.
There are many great scenes – the comment about the blonde dye, the blonde’s dance, the pheromones, the 50s-style underground, the other setups around the world (eg the creepy girl in Kyoto), the variety of horror monsters, and Mordecai. But it didn’t really work for me as a story – about halfway through a big “purge all” button is pressed (what a ridiculous button to have) and it’s just chaos from then on. I really hate the Topher stoner dude, no doubt it’s partly his fault too.
I suppose what I disliked was that the movie attempted to reflect on the genre and then completely backed off. It points out how characters fall into roles, bring some evil upon themselves, they die in a particular order, and maybe prevail – but that’s all. It contained some background on why this has to be, and juxtaposed a horror movie with a strange 50s day at work, but didn’t bring it anywhere or try to say anything. Perhaps the audience are like Great Old Ones, and the Director is literally a movie director, but that doesn’t go very far.