Sometimes you hear wildly different things about a movie from different people. Your friend loved it, while your cousin hated it and your girlfriend thought it was funny in a not-so-good way. And other times, it seems like you hear the same thing from every person you talk to. Mirrormask was one of those films for me. Choruses of "the plot is boring, but the visuals are amazing" seemed to echo from the heavens. I think most people short-changed the plot, and were a little too kind to the special effects, which makes the result.... a mixed bag, to be honest.
The story is simple, but endearing. The mother of a family of circus performers has some unnamed ailment that requires dangerous surgery. The daughter, who regularly escapes from life through her art, does literally that: she falls asleep and enters the world she has created from the drawings on her wall. She quickly learns that an evil princess took her place in the real world, and that she must find (Guess! Quick! OK, I'll tell you....) the Mirrormask to return both worlds to order. And in an Oz homage-that-is-almost-a-ripoff, all the actors who play the adults in her real life are the adults in the fantasy world as well. The dialogue is a little stilted and dry, with just enough humor and levity to keep the film from sinking into gothic boredom.
Now, for the special effects. I will say that there is an overabundance of imagination on display here. Also, considering the film's budget, the entire affair is fairly confidently managed. But you often get the feeling that you are seeing rough drafts of digital effects rather than their finished forms. Most of the CG work is very, very obvious. And while you could make the argument that this was a conscious decision meant to evoke the rough state of the girl's drawings, there are ways to achieve that effect and still develop a more polished product.
Overall, I enjoyed the movie, but not as much as I hoped I would. It is effectively the same movie as Return to Oz, except not quite as good. If that sounds appealing, dive right in.