This is without a doubt the most fantastic visual animation I've ever seen. It brought to mind i) nature scenes on Pandora in "Avatar", ii) lush vegetation jungle scenes from "Up!", iii) the whole valley turning green at the end of "Princess Mononoke", and iv) the infinitely graded colors in "Oz the Great and Powerful". (I watched it in 2D, and don't know what 3D is like.)
But visually it outstrips all of those. The plants are real ones we're familiar with (not imagined ones); scenes are incredibly detailed (not one fern but tens of them, not one blossom but hundreds); biological growth and decay is of individual plants seen up close (not a very long shot across a whole valley); and all the vibrant yet subtle colors appear in nature (not a fantasy world). Vegetation unfurls and extends as we watch, and it all seems perfectly realistic and believable. We see the whole process of burls developing on live trees in just a few seconds over and over. We see growth meristems probing for the best direction and expanding little by little. And we see the slight shifts in color that signal the beginning of more decay or more growth.
All the animation effects technology has already conquered --fur, musculature, waves, droplets, rain, crowds, flying, moving cameras, etc. etc.-- are also deployed virtuosic-ally in the places the storyline calls for them. From my aged (about 60) perspective, it seems suitable and enjoyable for all ages (although it's rated PG) ...and not because adults will see a different film as they understand the more salacious meaning of double entendres - there aren't any. There isn't any notable music nor abstract visual patterns nor references to fairy tales either, other things frequently associated with animations.
The story is decent too. It's a seamless melding of realities (such as a brusque taxi driver) with fantasy (tiny beings riding hummingbirds?). It proceeds organically, eventually incorporating pretty much everything that happened earlier (even things that appeared to be already completed or even unrelated). The typical joke is mostly visual, developing slowly over many seconds - no one-liners here. There are not a lot of the ironic jokes that have been prominent in many recent animations. (In fact this movie is often relegated to "kids film" or "family film", which makes me feel a little silly for enjoying it.) The ending is positive but not saccharine -- there's resolution ...but not of everything.
Comic relief is provided by a tag team of a snail and a slug. A typical gag is something about "eyes inside your head" or "everybody hide in your shell" (slugs of course don't have shells). I found it adequately funny (but not laugh out loud funny). Humor is a very personal thing though, and I suspect some of the more "with it" young adults will find it painfully unfunny.
The flights, the fights, the falls are gripping. This is edge of your seat stuff. And the tiny perspective casts familiar things in a new light: a mouse becomes a threatening giant, and a looming doggie kiss would mean serious injury or even death. Pick a theater with a really big screen and a newish projector, and sit toward the front. And if you're an animation aficionado plan to attend more than once. Also, sit through the end credits, as the level of detail and imagination in the background visuals --often throwaways or repeats, but not here-- is astounding.
