Scott Wise’s review published on Letterboxd :
Disney applies the “Marvel formula” to a relatively unknown (at least to me) comic book franchise heavily drawing from a blend of North American and Japanese influence, but somewhere along the way loses sight of what makes its characters endearing.
One of the major flaws of the film is its character development. It spends a great deal of time developing and shading the qualities of its protagonist Hiro and his companion, Baymax, all of which is incredibly rewarding. But it switches gears somewhere in the middle of the second act as it begin to introduce an expanded roster to flush out the assembled team. While the first act is dripping in emotion and rife with humour (though much of it is given away in the trailer), the final act is markedly different, with formulaic action set-pieces and uninspired character motivations. We lose the humour and sentiment that lets us engage with the main characters, while its supporting cast remains ill-developed.
Big Hero 6 seems confused about the type of film it wants to be. And because the film shifts from a really good place to a noticeable more boring one, the ultimate effect is that it veers wide of its goal. When we reach the final climax that seeks to be emotionally rending, it feels shoe-horned when it really should have felt cohesive and integral to the main thrust of the story.
That said, the film is staggeringly beautiful. The visually-dense San Fransokyo is breathtaking, and the character Baymax is refreshingly well-considered (at least initially). It’s not enough to save the film, but it does bring it some vibrancy that will surely captivate, even if the narrative doesn't.