I've had this film sitting on my shelf for years, got it when I getting into the beautiful Ghibli works but for whatever reason I never got round to watching it and then kinda forgot it was there - well after all these years I finally gave it a watch and iiiit was not worth the wait, sadly.

I'm going to reference the plot a lot here so obviously spoilers ahead.

It starts off interestingly enough with a sequence of abundant forest and these plant like dragon creatures erupting out of the moon and making their way to earth, and then that promptly ends and we jump ahead. In a very Ghibli like intro scene we meet our young hero Agito and his friend descending from their rickety village through the innards of a mountain to fetch water directly from the source, where they get caught by these mysterious 'druids', seemingly plant people, who obviously don't want them there. Then Agito manages to escape, going downstream until he reaches a room full of pods and awakens the heroine of the film Toola. Then quite bizarrely without explanation the druids seemingly decide to try and kill him as they vent the water destroying the complex, however he and Toola manage to escape.

So far so good, sadly after this it becomes a whole lot more vague.The two main issues the film is that the plot has no real meaning, and none of the characters are even remotely charismatic. The main event of the story is that Toola meets up with someone else from the past who manages to convince her (with quite little effort considering she's only been awake for about one day) to join him to work to return the planet to normal, conveniently too he worked with her father who was researching ways to reset the earth's ecology. This brings up two character problems, the first is that Toola so quickly decides the world needs resetting, and the other is that Agito's reaction is basically to go don his white knight cap and sets out to effectively kidnap her back, as she did willingly leave. So having spent about ten minutes of screentime together (she spends more time with a villager girl who takes a disliking to her because she thinks she wants Agito's babies despite having just met) they're separated and past this point most of their interaction together is yelling each others names.
Agito could have been an interesting character, it's revealed his pseudo village chief dad is part tree as he and several others gained the powers of nature (without explanation) and founded the village. This could have been used to give him conflicting feeling about how his dad is mutated while other people have normal families, but instead he's totally fine with it. Surprise surprise his dad dies and he immediately walks into the forest to get given those same powers, which the forest is totally cool to give him because they already know that Toola is the key to the planet reset.
The 'forest' in question is the most potentially interesting part of the film, as mentioned before you see these 'druids', mute warrior like beings made of wood and leaves, and these two strange green loli twin girls, apparent rulers of that part of the forest. However you never find anything out about any of this, they're just there for a couple of scenes, give some warnings to the village and grant Toola his power and then get forgotten.
It's unfortunate you don't see more of the twins as bar maybe Agito's friend they're the only characters with any sense of charisma in the film. Toola is mostly mute and sombre looking and gets one flashback that reveals nothing noteworthy at all while the bad guy isn't evil enough to be dislikeable and is even revealed to have a valid reason for his actions. Everyone else is either bland wise old guardian or just there. Agito doesn't start with much personality but when he becomes treeman he basically has none at all.
It's quite fair to say that the final part of the film is basically Akira but with tree powers, Agito rips and kills his way through the land to reach Toola and then body morphs himself into a tree to kill the bad guy letting Toola save the day, and of course her apparent and sudden love for him brings him back. There's a mountain base which somehow starts moving and is covered with laser guns and it all becomes very silly.

The plot problem is that it's all so meaningless, if this were a Ghibli film the whole thing would be a metaphor for humanities mistreatment of the earth and nature's fighting back, which I suspect is what the film is trying to get at - however, the film literally provides a scientific plot reason for the events that happen, there is no metaphor, all it is that humans took science too far and created angry sentient plants. Nothing behind Toola is explained, why she was frozen or her relationship with her father. Nor do we spend anywhere near enough time with our two leads to care about them or their relationship.

It's a shame really, the film has clearly had a lot of work put into it, there's many beautifully drawn background settings and there's some interesting location and vehicle designs, it's not un-enjoyable there's some decent action and it's not long enough to overstay its welcome (though being longer would certain help the plot), but the one dimensional characters and vaguely worthy but ultimately shallow plot spoil it.