Georgie described it as "an 'Alice in Wonderland' for the 21st century," and I concur. There are also distinct similarites with "The Labyrinth" (also a Jim Henson company production) but this dreamscape is informed by Freudian and Jungian concepts ("the shadow" is not just a dramatic phrase, here) and imagery from Breughel, Goya and Dali. One of the points of conflict is Helena's separation from her mother to become her own person--not an issue in "Alice."
One critic disliked the movie, which uses a mix of digital and traditional animation combined with live action, for not using "real" sets, models and puppets, instead of what were referred to as "blurry" special effects. That person did not get it. With mutiple visual textures and layered effects with backgrounds bleeding into foregrounds, the movie style is like some of the "Sandman" comics, with multilayerec collages and color washes in action. The occasional soft focus reinforces the dream-like effects. The one criticism we had was the soundtrack: occasional bits of dialog were hard to hear. Other than that, we considered it a masterful work and well worth seeing.
Rated PG for some scary images. The darkness effects and creatures are quite creepy. The subtext will be lost on children.