All in all - pretty good. I think it rises to being above average for what it isn't more than what it is. Good action and threads of danger but not too dark; although my 4 y/o was slightly spooked by the bad guys.
The title is far reaching as it will not stand the test of time as an epic movie; but it does relate an epic event in the fairy world that we get to watch.
Teen-ish MK (Mary-Kate) is sent to live with her father after the death of her mother. The mother and father split due to the dad's obsession with chasing a fairy world.
So it turns out the fairyworld is real and there's an ongoing battle between the fairies who bring life to the forest and some forces that are seeking to bring decay.
Every 100 years the fairies anoint a new queen. The selection ceremony is important and cannot take a shortcut for safety. The leafmen guard forces try to be prepared but get overwhelmed by the decaybringers and MK is drawn into delivery the seedpod to complete the ceremony when it blooms under the full moon.
The story works well enough. There are some well worn story elements - dead/missing parents, rebellious teen, etc; but they play okay. There is some humor for various ages (physical and word humor). I found the voice work to be good and fitting.
I think what lets this movie rise out of the sea of mediocrity is what it isn't. It isn't a tree-hugger movie - Ferngully, Avatar. This provided some good discussion on what a "tree hugger" movie is. The decay of the world isn't the fault of humans. Humans are not ignorantly wrecking everything or willfully wrecking everything. It isn't a tale of children needing to teach their parents/elders - How to Train Your Dragon, Cloudy with a Chance of Meatballs. It isn't moralizing.
Fairyland is nothing but the sunny country of common sense. It is not earth that judges heaven, but heaven that judges earth; so for me at least it was not earth that criticised elfland, but elfland that criticised the earth. I knew the magic beanstalk before I had tasted beans; I was sure of the Man in the Moon before I was certain of the moon. This was at one with all popular tradition. Modern minor poets are naturalists, and talk about the bush or the brook; but the singers of the old epics and fables were supernaturalists, and talked about the gods of brook and bush. That is what the moderns mean when they say that the ancients did not "appreciate Nature," because they said that Nature was divine. Old nurses do not tell children about the grass, but about the fairies that dance on the grass; and the old Greeks could not see the trees for the dryads. - GK Chesterton