I know people say this movie is a bomb, but honestly, everyone I know that is a fan/familiar with Tenacious D loved it. If you're not familiar with them, watch some of their old stuff on YouTube and listen to their music before you watch the movie, and I think you'll enjoy it much more.
I got this as a Christmas gift for my wife. Like me, she's a huge 5FDP fan. She was super happy to see it Christmas morning. We blasted this CD on the way to and from family gatherings. Epic. Simply epic!