It's amazing when comedy focused people really try.  It reminds me of comments I heard about the Starfellows, a brother duo who, for moments at a time, were really amazing musicians together.  They were brothers, though.  Real brothers.  The kind of brothers that would fart in a jar and dare the other to open it.  Every performance quickly devolved, but you could tell there was real potential there.  Here, Tenacious D ventures into the realm of seriousness (they do it a lot, more than the Starfellows) and the results are impressive.  Unfortunate they don't play the entire song, but that's okay.  What was performed was amazing.