I always thought The Fisher King should have been a better movie than it was. I still watch and enjoy it every time it comes on TV but I am always aware that it somehow doesn't work well as it should.

I agree with Bee-dubya-ell about One Flew Over The Cuckoo's Nest. It was a huge disappointment that the film was not made from Chief Broom's perspective.
(The scene where the chief throws the water cooler through the window to Jack Nietzchke's music is one of my favourite bits of cinema.)