To me this just seems to be another wave on the pop-culture phenomenon that has become Johnny Depp and Tim Burton worship. It all seemed to start when this whole "faux-goth" (offshoot of emo) thing started to get big these last few years.
The Nightmare Before Christmas re-emmerged as a popular film because of this movement, and Tim Burton is seen as a dark, and therefore appealing, director to this specific demographic.
And of course, with Depp as Sparrow in PotC, his popularity soars because they are good movies, and he does give a good performance, but everything gets blown out of proportion because "OMG JOHNNY DEPP IS HAWT" and he played a "dark" character in Edward Scissorhands, which, surprise, surprise, has some new popularity and merchandise just like TNBC.
Corpse Bride was, I thought, the culmination of this trend, namely, a Tim Burton/Johnny Depp movie, made to ride this wave even more because it featured the same stop-motion claymation that TNBC did.
Sweeny Todd appears to just be a continuation of this.
Tim Burton + Johnny Depp + Dark/Disturbed Character = Whinny faux-goth teens flock to the theaters in droves and add said character to the pop-culture hall-of-fame although its really not that great of a movie.
I don't think I really articulated this great, but oh well.
By the way, I'm not saying Tim Burton and Jonny Depp aren't talented, nor am I saying I don't enjoy their work. But, from what I've seen (Namely, those four years I spent in High School and all the time I spend online) they're way Overrated.
This thread doesn't help that imagine.
All that said, I didn't know Sweeny Todd was a play before a movie, and with that knowledge I know realize that this may actually have something going for it. Maybe not, but maybe.
Plus I love Alan Rickman.
Going to see the movie? Likely yes.