IMDb; Jim Henson Company; Muppet Wiki; Rotten Tomatoes; Sony Pictures; Templeton Gate; TV Tropes; Wikipedia
Caution: potential spoilers.
This came out in 2005, but I didn't see it until 2013. I remember when it was released on DVD, it was in a box set that also contained The Dark Crystal and Labyrinth, but I didn't get that (I own all three movies on individual DVDs). And... my understanding was that the main way the three movies were supposed to be connected, aside from being Jim Henson Company productions, was art designs by Brian Froud. However, now that I've finally watched the movie and read a bit about it online, it seems he wasn't actually involved in the movie (though he was considered for involvement). In fact, it was designed by Dave McKean, who also directed it and co-wrote it with Neil Gaiman. Also I should say the film stars Stephanie Leonidas, whom I became familiar with earlier this year as Irisa in Defiance. So it was interesting for me to see her several years younger (and human). Her character was like 15 in this movie, though I think she was around 21 when the movie was made. (I believed her as a teenager, though.)
So, anyway... Leonidas plays Helena Campbell, an imaginative and artistic girl who works in a circus, with her mother, Joanne, and father, Morris. They're struggling financially, but Helena doesn't care. She wants to have a regular life, which leads to an argument with her mother. Later that night, Joanne collapses, and is taken to the hospital. So of course Helena feels guilty about what she'd said to her. She does get to talk to her in the hospital, and their relationship seems to me to be pretty well mended. But later, Helena still feels guilty, because she didn't technically say "I'm sorry," though she did say she didn't mean what she said. (Seems kind of like a weak motivation for guilt, because in stories like this, characters often don't get a chance to even say anything at all to the person they've wronged. But whatever. She still has reason to fear her mother could die, which is a pretty big deal, obviously, guilt or no.)
Later, on the night Joanne is having her operation, Helena has a brief, strange dream, then wakes up. But she soon finds that she's actually in a much stranger dream, set in a very bizarre world full of very bizarre people and things. The first person she meets is a juggler named Valentine, who has a couple of associates that are soon destroyed by some kind of shadows. Or whatever. Helena manages to escape with Valentine, who will serve as a kind of guide in this strange world, though... he's not very reliable. Also, Helena occasionally sees glimpses of her own world, through windows. And she learns that someone who looks like her has replaced her in that world. And that person is an evil princess, who had stolen a charm that was needed in order to wake up the White Queen. See... this whole world is basically made up of stuff Helena herself had drawn, including a city of light and a city of shadows, each of which had a queen. Now that the White Queen is asleep and unable to wake up, both cities are beginning to fall apart. Meanwhile, the Dark Queen has sent out her shadows to search for her missing daughter, as well as putting up wanted posters offering a reward for her daughter's return. Anyway, Helena and Valentine set off on a quest to find the missing charm, which they eventually learn is something called the MirrorMask. And finding that will not only save the dream world, it will also allow Helena to return to her own world. However, the evil princess is destroying Helena's drawings, which will make it impossible for her to return, even with the MirrorMask.
I don't want to say how it all ends, or give any details of Helena's quest. I will say it's rather ambiguous as to whether it was actually just a dream or really happened... I actually have reason to believe it couldn't possibly have happened, but I also think... it couldn't possibly have been just a dream. Anyway, whatever it was, the other world was, as I have said, bizarre. So I liked it. The design of it all was pretty awesome, and there were some cool ideas. (I loved the riddling sphinx, because it was so different from the riddling sphinxes one is used to. I found the way Helena and Valentine each dealt with it very amusing. Though there were other sphinxes in the movie that were more dangerous than funny.) Of course, nothing really made much sense, and some critics will complain about the story being somewhat lacking, and say really the only good thing about the movie is the visuals. But personally I think it makes sense that the story doesn't make sense or have much of a cohesive thread to it, because it is more or less a dream, and dreams aren't really known for their cohesive plots. As in dreams, you can't ever possibly guess what's going to happen next, so that's something I appreciated about the movie. Aside from that... Helena and Joanne were both easy on the eyes. And I guess I can't think what else to say, except I'd totally understand if some (or most) people can't get into the movie, and I don't think it was great, but I certainly liked it.