Although this film has been around for a couple years, the English-language version with American voice actors was only released in the U.S. relatively recently, and I didn't get a chance to see it until today (mid-July 2011, near Boston Massachusetts).
The appearance of the animation is truly amazing.
It's layered 2D animation. The layering is used to great effect, for example when individual bushes apparently in the middle of a jungle suddenly move as though an animal were passing.
Like older hand painted cel animation, each area of each character is mostly a single color with no gradations - but there are tweaks: rosy cheeks, shadows, bushy eyebrows and the like, and lots of highlights on the boundaries between areas (instead of uniform width black lines). The backgrounds are indescribable except to say they're extremely rich. They look highly variegated but without obvious brush strokes, rather like water colors. But the colors aren't pastels nor translucent, and the patterns aren't limited to variations on just one or two colors. The overall effect is rather like impressionist paintings.
In fact the colors are so rich the comparison that came to my mind was the recent "Rio". Of course that huge budget and army of animators wins the color contest. But the fact the comparison even came to mind shows just how intense and varied the colors are here. (Are we talking about something qualitatively different when animated features cost more than $200 million?)
There's a liberal sprinkling of CGI effects: falling snow, dappled shadows, blowing smoke, explosions, flames, fog, fire, waves on the surface of the water, reflections, shooting stars, raindrops. They're seamlessly integrated into the visuals and the story.
The story has lots of very creative riffs, and touches on several potentially interesting themes (government corruption in South America, the huge gulf between the wealthy and the poor in South America, internal dissension sapping effectiveness, family tensions caused by tunnel-vision pursuit of money, possible extremes of global climate change, destruction of a pure environment by people, the disconnect between scientific research and current political actions, wisdom coming out of the mouths of babes, rural vs. urban, and so on). It even gets quite current a few times: one scene with a telemarketer calling on a cellphone right in the middle of a helicopter pursuit had me in stitches.
All the bits and pieces and possible themes, although each interesting in themselves, for some reason I can't analyze don't cohere into a terribly involving or memorable story. Don't worry about that too much, though. It's not a negative, not actively unpleasant; it's simply the lack of an expected positive. Just let the story wash over and through you while focusing more on the visuals.
One frequently used storytelling trope is starting a cliché but then taking it in an unexpected direction. An old hag gives an attractive ripe fruit as a present - but it's given with the best of intentions rather than being the poisoned apple we expect. A falling drop of water at first appears to be a tear signaling the start of a ridiculously sentimental bit - but it quickly turns out to be the first raindrop on a shower instead. And so on...
The English translation and voice acting _appear_ to be fairly good, but are not memorably outstanding. (I wasn't able to see subtitles nor listen to the original sound track to compare though.) Double entendres and puns -the bane of mediocre translations- come through quite clearly. (For all I know, the English sound track _could_ actually be a crisper, punchier improvement on the original.) There's something for every age. Little kids will probably laser in on how independent and brave Mia is while at the same time she's so very close to her parents. Kids will probably never even notice some adult parts, such as Grandma's going on vacation with her "boy toy", or the boy toy's introductory line of dialog that seems innocuous at first but's a bit crude when you think about it.
One refreshing change is the "monsters" are silly almost beyond belief. We've come to expect monsters to be if not somewhat foreboding, then at least rather dangerous simply because of their largeness. But these monsters seem more like a cross between Calvin and Hobbes and Swiss cheese.
The boundary between "reality" and "dreams" is purposely porous and vague. Sometimes we don't know whether what we're watching is imagined, dreamed, magic, or just exaggerated ...and it doesn't matter. By the time we see an upside down tree with its glittering leaves _below_ the surface, it seems perfectly normal.