I'm a huge fan of Gilliam, but I had heard enough about this movie to know what to expect - Gilliam at his most mediocre. But to be fair, the movie isn't nearly as bad as people are making out. It's got a lot of dud moments, far more than any other Gilliam movie I've seen, and it takes a long, long time to get going. But when it does (roughly around the third act), it is almost worth the previous hour or so of drudgery.
Think of it as a panto writ large and you'll enjoy it a whole lot more.