Tim Burton's Sweeney Todd had a lot stacked against it: the commonly held Hollywood belief that movie musicals are still a big risk (especially gory, R-rated ones about scorned barbers who turn murder victims into meat pies); the potential backlash from the film's built-in fanbase, Steven Sondheim devotees who consider Sweeney among the composer's best work; Burton's generally hit-or-miss record; not to mention the fact that no one had ever heard Johnny Depp sing until just before shooting began. Somewhat surprisingly, though, the picture not only does justice to its source material - it's one of 2007's best.
To answer any initial questions, yes, everyone in the cast sings well, if much lighter and more airy than we're used to in its Broadway incarnations, where the show is basically an opera. And yes, some of the stageplay's flow is lost in translation to the screen (particulary, early on), but this is a decidedly different beast, and is as exhilirating as any version prior.
The color pallet and set design are pure Burton, and the director's considerable vision turns out to be a great match for the piece. While appropriately over the top at times, Sweeney is equal parts scary, pretty, and funny, as it should be. Although Burton mostly shows restraint, the film's first bloody scene is nearly ridiculous in its grotesqueness (I'm not complaining). Violence - even when larger than life - is essential to the story of Sweeney Todd.
Depp understands this, and while Helena Bonham Carter certainly looks the part of Mrs. Lovett (the owner of a struggling London pie shop), he inhabits the role, conveying with his eyes and body language what other actors have done with a house-shaking voice. Rounding out the cast are Alan Rickman, satisfyingly creepy as the judge who wronged Todd, and Sacha Baron Cohen (aka Borat), brilliant in his turn as Pirelli, Todd's would-be barber competition.
Ultimately, Sweeney Todd is one of those movies that gives one hope about Hollywood - that major studios and filmmakers are still willing to take risks to serve great stories.