I was very curious to see this movie, given that it had been nominated for an Oscar in the Best Animated Feature category along with Cars and Happy Feet, and that it had received very good reviews.
The story is interesting, original, and well developed, but I wasn't crazy about the animation. Given that two of the producers were Steven Spielberg and Robert Zemeckis, I thought they could have done better, especially since Cars was released that same year and it was eons better.
What I didn't like was the utter abnormality in the movements of virtually every character. The characters are "human," but they don't feel human when they move. Human animated characters have been drawn before, which much better results. Even simple 2D animation has achieved better results as far back as 1937's Snow White, the first full-length animated feature ever.
Here, a bouncing ball, a walking kid, or a person gesticulating, don't look and feel the way they are supposed to. It's like they live in a world with a different set of laws of physics. I read somewhere that making an animated character's movements feel real to the human eye is a challenge, precisely because when we look at something moving, we have an expectation of how it should look, even if it's animated, and if what we see doesn't meet our expectations, it feels weird, and it jolts us out of the story.
That's exactly how I felt over and over while watching this movie. I do hope that the effect was intentional on the part of the filmmakers, because otherwise they failed miserably. Human or animal, 2D or 3D, I've seen much better animation than I've seen here, for years and since. Even in a stop-animation movie like The Nightmare Before Christmas, the characters move more freely and naturally than here. Hell, even Cars's cars look more realistic than Monster House's children!!
And that was my tirade, at the end of which I do want to point out that the movie is good, the script solid, and the whole experience entertaining. Do watch it, even just to see what I mean.