This film is visually stunning - it's almost like watching a painting in motion. Everything about the visuals, from the sets to the costumes to the lighting to the camera angles, contributes to a surreal and rather otherwordly, while still dark and gritty, atmosphere - somewhat evocative of Gormenghast.
The plot has enough twists and turns to keep you constantly guessing, and frequently confused: Is Vidocq dead, or alive? Were the murdered men victims, or villains? Or pawns in something larger? Are we looking for a mad scientist, or an urban legend brought to life? Is the political unrest in Paris related to the case, or just a backdrop for it? It borrows elements from both science fiction and fantasy as well as being rooted in the detective genre.
Now, I probably have a higher than average liking for twisted, fantastic, genre-bending movies that make one's brain hurt, but even so, there were some serious holes in the plot, or at least things that never really were well explained. So viewers who place a high priority on logic and consistency may find it a frustrating experience. But overall I very much enjoyed it, and some of the visuals will be with me for a long, long time.