When I first saw the preview, I thought "I have to see that. It's going to be hilarious." However, now that I've seen the preview about 100 times, I think I changed my mind. I thought there was something familiar about the Nacho Libre character and then it hit me - it's Pedro from Napoleon Dynamite! Sorry, but I don't think I can take an entire movie of that.
I'm a big Jack Black fan, but I think this one will end up more like Envy than School of Rock.