Just to add some comic perspective: Big Hero 6 was supposed to debut in an issue of Alpha Flight, but instead they premiered in their own miniseries, Sunfire & Big Hero 6 in 1998. The premise of the series was that Silver Samurai (a character who would be familiar to longtime X-Men / Wolverine fans) had been given the task of forming a national superhero group for Japan, similar to Alpha Flight of Canada. However, the main characters of the series were the child prodigy Hiro Takachiho and his home-made robot Baymax. These two also happen to be the main characters of the movie. In the next miniseries, Big Hero 6 (2008), Sunfire and Silver Samurai were out, and the group had gotten the same roster that was later used in the movie.
I don’t know exactly how much power Disney has over Marvel as the parent company, but I imagine that they can’t just take any concept they like and do as they please. If Disney was allowed to make a movie out of a Marvel concept, it was probably because Marvel felt that they had no more use for it themselves anyway. Marvel Comics didn’t even bother to print a new edition of the BH6 trade paperback in time for the premiere of the movie.
On the whole, there are few traces of Marvel in the movie, not even their film logo is included. The "Man of Action" studio is credited are the creators of Big Hero 6, and sure enough; Steven T. Seagle and Duncan Rouleau, who created Big Hero 6, are members of Man of Action. They also created the characters Hiro, Baymax, Honey Lemon and Gogo Tomago. Wasabi No Ginger and Fredzilla, who are also in the movie, were created by Chris Claremont and David Nakayama for the second BH6 series, but they are not credited.
That said,, the movie Big Hero 6 only loosely based on comics. The names are the same, and the character designs have at least a little resemblance, but besides that, Disney stood very freely. The story has been moved to the fictional town of San Fransokyo, an obvious fusion of San Francisco and Tokyo. The superheroes have become engineering students, and Baymax has become a doctoring robot that Hiro took over from his brother. And while the heroes were all Japanese in the comics, they have become multi-ethnical in the movie
I won’t go into detail on how each character has changed, since most of them aren’t that well developed anyway. They all get some funny and charming moments (except Gogo Tomago, who comes across as rather uninteresting), but once again Hiro and Baymax are the real stars. Hiro’s an orphan - Not that it’s important to the story, in fact it’s almost as if he was made an orphan just because it’s a Disney tradition. Baymax has become more family friendly and iconic. He looks like a cross between the Michelin Man and a teddy bear, and has a classic "good-natured and naive robot" personality. Even after Hiro has given him battle experience and armor, he looks kind of cute and cuddly. It seems inevitanle that Baymax will be the most memorable thing about this movie.
BH6 is Disney Studios’ first own superhero movie; you might remember Brad Bird’s The Incredibles (2004), but that was made by Pixar. Compared with the latter, BH6 is definitely more kid friendly: the violence is less brutal, and the whole atmosphere is brighter and lighter. For many superhero fans who liked The Incredibles, BH6 will probably seem a little unsophisticated; the story is simpler, the details are fewer and the surprises are few. Disney needs to realize that it's difficult to conceal who’s the villain, and that the longer you keep them waiting, the easier they will see through the it. Furthermore, the villain of this movie gets too little time and space to become interesting, and his motivations are also shaky.
The film's strength, apart from Hiro and Baymax’ charms, lies primarily in visuals; San Fransokyo is a radiant, multifaceted, and exciting city. I cannot imagine any fictional Disney location I've ever wanted to visit more. Although the city has its share of destruction during the movie, BH6 is something as original as a superhero movie where the setting does not look like a permanent war zone or a coherent, criminal slum. It’s a movie that celebrates progress, and it does so in a far more convincing and heartful way than one of Disney Studios’ earliest experiments with digital animation, Meet the Robinsons (2007)