It is a fairy tale, with a light magic-realistic touch, balanced by an amazing amount of "this really happened" (which you'll have to go learn yourself; it isn't brought up in the movie). Or, ask me about it if you don't mind spoilers.
The plot has some nuance, which I appreciated, though the acting could have used a lighter touch- everyone was capable in their roles, but nearly all of the characters felt cartoonish at times.
The train station, clock works, movie studio (walled in glass to let in light- apparently historically accurate) and Paris street scenes are all gorgeous. Visually, I loved it. This is the first movie I've seen where the 3d truly enhances the art, rather than feeling to me like a gimmick. (I saw and liked Avatar, and I won't argue with somebody who felt this way about Avatar- but I'm a "gears, steam, and clockwork" kind of guy, rather than "blue alien jungle". TMI? [hush!])
What else to say? I don't think it passes the Bechdel Movie Test- there are various scenes of women talking to each other about men. I wonder if this was different in the original novel or a Scorsese touch. Oh- perhaps I'm wrong- a women talks to a girl (and boy, but mostly the girl) about how wonderful it had been to be an actress; that might count.
Anyhow, I am glad I saw this in the theatre.