Sweeney Todd: Singing
But instead, I will direct you to this excellent article at the NY Times, which articulates what I wanted to say in much more coherent fashion than I probably could have.
I will echo all that author Anthony Tommasini has to say in this piece, especially that while some have said that Johnny Depp's singing voice was adequate to the task, I was bowled over with how impressive it was, how emotional and intimate.
Anyway, read the article at that link. It's worth your time to understand the difference between the film's musical style and the stage's version and why the style the filmmakers chose is the right one for a film such as this.