I would have to classify this as one of the least enjoyable movies I've ever watched. There were many wonderful ideas, including imaginative locations and vehicles, and the basic premise of the story had merit, but the execution seemed *miles* off target.
Firstly, the main character looks to me like a little boy, somewhere between 3 and 8 years of age. The opening scenes find him running and playing, with suitable childish glee. I was both startled and disappointed, then, when he began laughing with the voice of a young teenager. The voice felt utterly wrong for the character - like sci-fi scenes where a woman speaks with a man's deep voice. We are also supposed to accept that a considerable amount of time passes over the course of the film, but his character never looks or sounds any older. His childish appearance is made all the more disturbing by the fact that he is given a love interest (whom we are supposed to like, but whom I found to be repulsively creepy).
One of the biggest overall problems with the film, however, is pacing. Things just don't happen at a natural tempo. This is true both in the bigger scope of the story, as well as within the context of particular scenes or camera shots.
A prime example of this would be the many scenes which simply showed two characters doing something and laughing. The purpose of such scenes is to establish that the characters are bonding, and having a good time together. This could be accomplished in about 5 to 10 seconds. Unfortunately for the viewer, these scenes are drawn out to a minute or two in length. At the end of the scene, the characters are still in the some location, doing the same thing, and nothing new has been presented. This extra time does nothing to advance the plot, and very quickly becomes tiresome.
Not only is this laughter hard to justify from a story-telling standpoint, it's also hard to accept it as believable. When people are enjoying an activity, the normal human response is not to laugh, but to smile. People only laugh for extended periods (without anything funny happening) when they are exceptionally tired or drunk, and the laughter in the film didn't seem to be caused by either of these.
In many of the shots, the animation was also just *slightly* too slow to feel natural. Other shots were clearly intended to be slow-motion, but these lost much of their effect and believability, because motion blur wasn't added.
It is also worth mentioning that a substantial portion of the dialog in the film consisted of single words. The characters showed a tendency to say things like "oh" "ah" and "ooh", in response to their environment, to a degree which was excessive, annoying, and rather silly. They also liked to answer questions with single word answers, whenever possible.
If I'd seen the movie more recently, I'm sure I could quickly double the length of these comments. Since it was a few months ago, however, (and I don't plan to watch it ever again,) I shall conclude my ramblings with the recommendation that you go and watch this, as a spectacular example of how *not* to make a CG film.