'Big Hero 6' is a fine blend of sweetness and spectacle

'Hero' centers on teenager Hiro (voiced by Ryan Potter), who encounters a robot named Baymax (Scott Adsit). The movie's first half is buoyant but the film slowly slides into familiar comic book-movie ruts.

As the Disney-Marvel mash-up "Big Hero 6" moves toward its big-action finale, the images will look strikingly familiar. A supervillain wreaks havoc. A portal to another dimension looms. A showdown goes airborne over a metropolis.

It could be the finale of a dozen superhero films, with one difference: "Big Hero 6" is animated. But the majority of comic-book films are also computer-generated, particularly their large set pieces. Never has that been clearer than witnessing just how similar such scenes look as out-and-out cartoons. It's a little like seeing that the superhero has no clothes.

The 3-D "Big Hero 6" is loosely based on a little-known Marvel comic about a team of superheros. Crafting a more kid-friendly version, Disney (which owns Marvel) has focused on one of the heroes, the aptly named Hiro Hamada (voiced by Ryan Potter).

With his older brother, Tadashi (Daniel Henney) and their aunt Cass (Maya Rudolph), the 14-year-old Hiro lives in San Fransokyo, a beautifully rendered fusion of Tokyo and San Francisco, full of both nighttime neon and steep-hilled, Bay-area panoramas.

Hiro, whose parents died when he was a toddler, is an avid gamer happy to use his technical wizardry hustling unwitting competitors in underground "bot fights." His tiny, gingerbread man-sized robot makes mincemeat of more hulking machines.

Tadashi disapproves but doesn't lecture Hiro, instead casually exposing him to his college, San Fransokyo Tech. Though Hiro initially dismisses it as "nerd school," he discovers it to be a vibrant breeding ground of invention. He's wowed by Tadashi's schoolmates – Wasabi (Damon Wayans Jr.), Honey Lemon (Genesis Rodriguez), Gogo (Jamie Chung) and Fred (T.J. Miller) – and their gizmos.

None is more impressive than Tadashi's robot, a marshmallow balloon "personal health care consultant" named Baymax (Scott Adsit), created with a "non-threatening, huggable" design. He's like an Obamacare dream, had the president drifted off during a Michelin commercial.

With a quick scan, he can diagnose any ailment. Looking Hiro over and detecting mood swings, he pronounces: "Diagnosis: Puberty." When his battery life wanes, he loses air pressure and begins to drunkenly slur his speech.

In short, he's an irresistible Disney supporting player, one who will give Groot, the soulful treelike alien of "Guardians of the Galaxy," a run for sidekick-of-the-year.

After a mysterious fiery accident at an invention showcase, Hiro and Baymax set off on an adventure that will gradually gather all the expected superhero conventions, slowly draining the movie's innovative Silicon Valley spirit.

So buoyant is the first half of "Big Hero 6" and so colorful is its bright, Japanese anime-inspired palette, that the film's slide into familiar comic book-movie ruts comes as a disappointment. Could it not have stayed in its rich robotics world as a high-tech high-school tale? Are such Earth-bound stories no longer possible for big-studio animation? Can't a kid grow up without flying up?

Directed by Don Hall ("Winnie the Pooh") and Chris Williams ("Bolt"), "Big Hero 6" is a fine blend of sweetness and spectacle, East and West. The meeting of Disney and Marvel sensibilities, though, is a more mixed union. When the young Hiro and the lovable Baymax strap on the body armor, girding for battle, the movie's charms are camouflaged.

"Big Hero 6" is preceded by a lovely little short, "Feast," a tale of a Boston Terrier's devotion to his owner, told exclusively, and cleverly, through mealtime. It makes for a tasty appetizer.