Princess Mononoke (1997) is written and directed by Hayao Miyazaki. It has a similar theme to a lot of other Studio Ghibli movies (Castle in the Sky and Naussica as examples), the battles between humans and nature. The story follows the adventures of Ashitaka, who is a brave young warrior who battles a giant cursed Boar in the opening scenes of the movie. Mononoke means monster or spirit.
(This is the Japanese movie poster. I think you can see why they changed it for the US audience. A girl with a bloody mouth and a knife would not sit well on the walls of the local theatre)
The village elders convene and determine that he must journey to the West in order to find out what is happening there to drive evil their way, and possibly find a cure to his curse, which otherwise will kill him.
Arriving in the fortified mining colony of Tatara, he quickly wins the trust of the people there with his fighting skills. The town is battling the creatures of the forest, and San (a girl raised by a giant White wolf god) who are trying to stop the humans from chopping down all the trees to mine iron ore. Lady Eboshi (voiced beautifully by Minnie Driver in the English version), is leading the fight against the forest with her army and with guns. It turns out a pellet from one of these guns is what turned the giant Boar evil in the beginning.
Ashitaka meets and gains the trust of San which leads to animosity when he returns the town. There is conflict between the creatures live in the forest and don't want the trees to be chopped down and the humans want to destroy the forest in order to mine and build their town into a powerful and rich city. Even the humans are conflicted and complex characters.
Much of the movie is action packed battle with packs of giant creatures swarming through the forest. Ashitaka rides an Elk which is beautifully drawn and animated. The giant Wolf gods, Boars and the spirit of the forest are all believable yet extraordinary.
This is a new favourite of mine, a deep and sophisticated story, but quite light and filled with humour. I'm surprised I didn't come across it earlier, because according to the wikipedia page it was a huge hit in Japan; the highest grossing movie until Titanic in fact.