I have to admit to knowing nothing about the film going in -- only that Ledger's role was "finished" by Johnny Depp, Jude Law, and Colin Farrell -- and figured it was a 19th-century story about a scientist.
Boy, was I wrong. But there's a lot of 19th-century stuff in there. It's a magnificent piece, the use of other actors playing Ledger's role works beautifully, and it's the usual Terry Gilliam amazingness, with lots of torn rags hanging off things like he always has.
Christopher Plummer, Ledger, and Ledger's stand-ins are all very good. Lily Cole is radiant as Valentina. But the show is stolen by Verne Troyer as Percy and Tom Waits as Mr. Nick (the devil, truly).
The movie is an absolute delight, a visual feast, and pretty much the usual story as to what happens when you make a deal with the devil. It's not Gilliam's best, and you can tell he's trying to hit notes he's hit more successfully in other films (as an example, there's a lot of Baron Munchausen in Plummer's Parnassus, but John Neville made it work a bit better than Plummer).
Right now, it's only playing in NYC and LA, probably in the hopes of some Oscar nods. Waits and Troyer deserve them, but won't get them, in all likelihood.....