"Astro Boy," which opens Friday, is a beautifully animated retelling of the character's early days. Though there are some starts and stops, the film is mostly enjoyable as it updates the classic Japanese hero.

Sometime in the future, the affluent have left the surface of the world for a floating haven called Metro City. Metro's scientific advancements are credited to Dr. Tenma (Nicholas Cage). According to an instructional film at the start of film, Tenma advanced robotics to a point where people live safe, leisurely lives. Of course, that leisure threatens the tenure of Metro's President Stone (Donald Sutherland). As the story begins, Stone and Tenma are on their way to see a demonstration of Core technology discovered by Tenma's friend and colleague Dr. Elefun (Bill Nighy). While the Blue Core could power Metro and all its robots for generations, the Red Core could power the war machines Stone needs to lead an invasion of the surface.

During this a test of the red-core in one of Stone's battle robots, Tenma's son Toby is vaporized and the Blue Core is apparently destroyed. While grieving the death of his son, Tenma designs and builds his most advanced robot ever; a splitting image of Toby. Though Elefun tries to talk him out of it, he gives the Blue Core to Tenma in order to power the robot. It awakens with all of Toby's memories and assumes it is, indeed, Tenma's son. The doctor does nothing to dissuade this belief at first.

It soon becomes apparent to Tenma, however, that the robot is different from Toby and recoils from it. He asks Elefun to deactivate it just as the robot begins to learn about some of its capabilities. The robot flies away and is discovered by Stone. After a daring chase, the robot ends up on the surface of the Earth where he is adopted by a group of children lead by Cora (Kristen Bell) who have no idea it is a machine. It is here the robot adopts the name "Astro."

The kids take Astro to their surrogate father, Hamegg (Nathan Lane), who restores robots to fight in an arena he also owns. As the kids restore another robot, Zog (Samuel L. Jackson), Hamegg discovers Astro's true nature. While Cora and the kids come to terms with Astro's robotic origins, he must fight for his life in Hamegg's arena and, eventually, face Stone and his Red Core-powered Peacekeeper.

The film features some of the best animation outside of Pixar. It seems just as in traditional hand-drawn animation, computer characters appear more natural the more they caricature human movement and less try to mimic it. This principle is on display in "Astro Boy." While all the characters have the gelatin feel that seems to part-and-parcel of the process, it never becomes jarring. The color in the film pop. Metro City glows and even the surface, which should be dominated by dingy browns, features an impressive palette.

Every fight and chase in the film is beautifully realized. Astro's initial flight from Stone's forces is a great mix of energy, comedy, and rich detail. His eventual fight in Hamegg's arena has an equal degree of craft. The fight with the Peacekeeper is impressive as well.

The writing of the film is, perhaps, its weakest element. While each individual sequence is well-made, getting Astro from one setting to the next is often confusing or arbitrary. The best example of this is Hamegg's arena. While Hamegg is initially portrayed with genuine warmth toward Astro and the other children, his mad fight promoter persona seems to come from nowhere or an earlier draft where the character was meant to be clearly evil. Though his intentions for Astro are foreshadowed, the eventual turnaround is quite abrupt. Similarly, he chooses to abandon Cora and the children for no apparent reason. It seems as though Hamegg completely changes personality because the plot demands Astro fight in the arena and, therefore, the character development is abandoned.

There is a similar moment when Stone orders Tenma to deactivate Astro and retrieve the Blue Core. Up until this moment, Tenma has recoiled from the machine, but here he suddenly decides the robot is his boy. There is no build-up to this change of heart.

These concerns do not sink the film, however, as it moves at such a brisk pace. While there is certainly a "check-list" feel to the writing, it will not be as noticeable to its intended younger audience. The film also does a nice favor to adults as most of the humor is born from characters and situation rather than pop culture references. The film also refrains from the "loudness" of most animated films aimed at children. It respects its audience and this is most apparent in the fact is never shies away from Toby's death. The conflict between Astro and Tenma is the fact he is not an exact duplicate of Toby and it sets the rest of the film in motion.

The voice cast is well-chosen. Though all are name actors, most fold so seamlessly into their characters, you are rarely distracted by their presence. Eugine Levy's robot butler, Bill Nighy's Doctor Elefun, and Freddie Highmore's Astro are all well-voiced and fluid with the story. Even Samuel L. Jackson disappears as Zog. In the early parts of Hamegg's screentime, Nathan Lane is so genuinely affectionate as the character, his turnabout becomes more abrupt. The one exception is Nicholas Cage, who never quite seems to mesh with Tenma. In his every line is the acute awareness that his is Nicholas Cage, star of "The Wicker Man." Again, not a problem for younger audiences, but it might be jarring for the adults.

The film does take liberties with the source. Tenma never gives into sinister urges. Hamegg is not so solidly evil. Most troubling to fans will be the lack of interaction between Elefun and Astro. Though Elefun becomes Astro's guardian and mentor in the original stories, here he rarely even speaks to the robot. In this version, Tenma is intended to be Astro's father figure. Least troubling is the addition of Cora and other children. A mix of Artful Dodger and Pan's Lost Boys, they make a nice supporting cast for Astro in this outing and work well as much of the story concerns Astro's search for a home.

"Astro Boy" is an interesting experiment from Imagi Studios, their first effort since 2007's "TMNT." While lacking in the story department, the film certainly illustrates a dedication to quality animation that does not resort to the cheaper gags one tends to find in modern family films.