It was the pacing. Honestly, about halfway through the film I was wondering what was "off" about it. It flowed like chapters from a book rather than a movie. Once I realized that, I was able to enjoy it further.
Adams did have quite a bit to do with the screenplay, and I think he might have made a few changes, but not many.
He was once asked if the film would be made for his British fans or for American movie goers. He said American movie goers, there were more of them. When the British reporter protested that as many Brits would go to see it as Americans, he responded that the reporter better get busy making more Brits if he believed that to be true.
Tangentially, Friday my 18yob and I saw Kung Fu Hustle, and laughed quite a bit. If you saw and enjoyed Shaolin Soccer -- this is better. Chow pulls out all the stops trying to drop your jaw and make you laugh, and mostly succeeds. I only regret the very last scene; if it had ended with the immediatley-receding, I'd've gone out happier. Maybe it's an Asian-humor thing. But still, very fun time, very energetic and electric. More of that spirit and pacing would have made HG more fun.
Dan