See I disagree, thought the start was very clever in the kind of way Scream was with the satire about the genre. I thought there was 10mins when they got out of the lift where it went silly which somewhat ruined it for me me before it brought it back together for the ending
The thing that confused me at the start was the shield around the facility, that made me think it was some kind of virtual reality type scenario. I thought the monsters were robots and couldn't figure out why there was blood when they killed them.
As a huge Buffy fan I can see all the good things Whedon does in the film, but my train of thought was derailed and when I finally realised I thought what a waste of an opportunity.