The previous review totally missed the point. The movie IS Zak Penn's; he wrote and directed it. There was no Loch Ness movie; Herzog was playing a role in this mockumentary.
If you've ever seen any "making of" features about Herzog and his movies (or "My Best Fiend"), the understated way Herzog plays his part is completely believable and makes the movie absurdly funny. So many of the difficult situations Herzog finds himself in during his directing travails are often described by him in hilarious understatement in these other features, which lends itself perfectly to this type of satire. However, without being aware of this aspect of Herzog's personality, this movie won't be nearly as amusing.
Zak Penn is an amazing man just for being willing to make himself look like such a total idiot on film. Considering a large part of the cast were not actors per se, they did a fabulous job of making it look real, even after the point where the happenings have become so absurd you know it can't possibly be so (I already knew going in that it was all staged, which made it even more entertaining to me from the get-go).
And just in case by the end you didn't get that the whole thing was fake, the jaunty music over the end titles should clue you in.
I have not listened to the commentaries yet, but there is one set where they comment on the documentary as if it was real, and another set that's the real commentary on the making of the mockumentary. Just that idea earns this DVD five stars, plus all the extras hidden on the DVD. But even without that, it was a truly entertaining movie that I'm itching to see again. I had many moments of out-loud laughter, which is something that does not often happen to me with movies.