1. It has all the creepily ghoulish macabre that every horror film deserves
Not only does this film achieve success in the sublime performances that help anchor it, but it also gives the audience a good-old-fashion horror show, while keeping it's viewers at the edge of their seats. It's richly dark film-noir-esque mood may be a little uneasy for those who are not a fan of the genre, but it works on a thrilling and (ahem) bloody story that reshapes Gothic musicals.
2. It has an engaging story line
For those unclear of the plot of the film, it begins in London with a mild-mannered barber named Benjamin Barker (Johnny Depp), his wife Lucy and infant daughter Johanna. That's right. Barker has everyone of man's ambitions: perfect wife, beautiful daughter and good-paying job. Nothing can go bad for him. Right? Well, that is until the villainous Judge Turpin (Alan Rickman) banishes barker to a penal colony in Australia, so that he can "have his way" with Barker's wife and daughter. Fifteen years later, Barker returns to London assuming the alias Sweeney Todd and ready to enact his vengeance. This plot easily rises above the typical revenge story ("Taken 1, 2, 3") where all the plot to those stories is "someone has been wronged some way and they want revenge". That's all there is to them, but Sweeney Todd has more layered characters and plenty more character development spread out evenly in the story, ranging from Todd's transformation to a good-nature barber to homicidal, remorseless killing machine.
3. The performances are wonderful
Depp easily fits the profile of this Hugh Wheeler creation. This is easily his best performance in ages because it not only showcases his abilities as an actor but as a singer. The supporting cast works just as well. Helena Bonham Carter may look like a homely, lifeless vampire, but she's splendid as Nellie Lovett, who helps Todd get back on his feet by allowing him to re-open his barber shop right above her pie house.
4. Tim Burton gives stellar direction behind the camera
Burton expands his creative genius for Gothic works into this Sondheim musical, masterfully. Not only does he utilize the same eerie feel and technique used in his previous films ("Edward Scissor-hands", "Corpse Bride", and "Sleepy Hollow"), but he gives more dimension to Sweeney Todd by detailing Todd's background with visual imagery and subtlety. This movie is the perfect vehicle for Tim Burton to showcase his gothic techniques even further in film. It's kind of hard to believe he's going to be directing a live-action reboot of Walt Disney's "Dumbo" pretty soon.