Part of the problem is the fact that Sweeney Todd is actually quite a political play, and this possibly doesn't really come out in the film. The other problem is lots of things possibly work far better with a live audience, and Burton may not have found a way of building that relationship with a cinema audience.

Apparently, because she was pregnant, Bonham-Carter's breasts were a continuity nightmare - I was engrossed enough not to notice.

Sweeney Todd is a strong score - it's just not your hummable song - and sadly, they cut The Ballad of Sweeney Todd - which is what the audience tends to come out humming from the play.