"MirrorMask" is, unfortunately, a perfect illustration of the fact that the talents of illustrators and comic book storytellers don't necessarily translate well to the big screen. For every successful Terry Gilliam, in other words, there's a Dave McKean - someone who knows how to put striking visuals on the screen, but who fails to back them up with intriguing story or compelling characters.
"MirrorMask" is about Helena, a girl who finds that she has entered a dreamy fantasy world on the eve of a life-changing event. This film is part of an old genre - running the gamut from "Alice in Wonderland" to "The Wizard of Oz" to "Labyrinth" - and mostly follows the blueprints. For instance, Helena soon meets Valentine, a performer, and the duo find themselves desperately searching for the McGuffin of the plot, the MirrorMask.
The performances in general are good, with Stephanie Leonidas' Helena satisfying most of the coming-of-age character points that must be hit. The pervasive CGI in the movie is done well, and often the results are astonishing, good-enough-to-frame images. The jazzy score from Iain Ballamy would be out of place in most movies, but it fits fine here.
The main problem with the movie though, at least for me, was that there's not much to it. The story is quite simple, there aren't a whole lot of characters (and even fewer characters with significant amounts of dialogue), and the whole thing ends up feeling a bit...empty, almost more like a student film project than a real movie (imagine "The Wizard of Oz" without the memorable song sequences, and where Dorothy just meets Scarecrow and never meets the Lion or the Tin Man). It's a chore to just sit through one disconnected happenstance after another.