TLDR: This is one to skip. It's both mindless and devoid of entertaining action - unsatisfying in every regard.
I was lucky enough to get in to the U.S. premiere at Anime Expo, but my expectations weren't nearly low enough for this. Miyano Mamoru tends to be attached to good projects, but this one felt like a mistake.
The movie makes use of the title of a very famous piece of Japanese literature by Osamu Dazai, "No Longer Human." Unfortunately, any relation this movie has to that book is all surface-level. The character names are mostly used (Youzou, Horiki, Takeichi, Hiiragi), but their personalities and motivations don't really draw on the book at all. This in itself is not necessarily a bad thing; plenty of adaptations of written works become something entirely different on the big screen.
In this case however, the result doesn't have much merit on its own. The movie is a vague and generic story about humans succumbing to some kind of corruption that turns them into monsters, and the oppressive government and police agencies that keep society running as they see fit. The art style gets the job done but it's not a standout. It's average 3DCG animation, average character designs, and the main physical transformation that Youzou undergoes is fairly generic in appearance. Guyver-esque is how I'd describe it.
I'm not going to go into spoilers really, but the main takeaways for me were as follows:
1. The character motivations are weak/cliche (hero wants to be good, villain wants power and destruction, good girl is sweet, submissive, kind).
2. The story doesn't really go anywhere interesting, and at times it's completely nonsensical. The first two acts aren't awful, but they don't lead to a satisfying conclusion in the third. I would describe the story as both incoherent and unmemorable. It slipped off my brain an hour after I saw it.
3. The only reason they named it after Dazai's novel was for marketing. Crossover appeal to both fans of the novel and Bungou Stray Dogs was definitely the primary factor, because they didn't even try and address anything the book focused on. Youzou attempting suicide is window dressing. A throwaway gag. "He tried to do that in the book!" "He does that in the show all the time haha it's so funny." I'll admit the book is impossible to film or adapt to a movie, or at least very difficult, but they could have at least done something that tapped into one of its core acts, like drug dependency, or being unable to identify socially with other people. They didn't.
Before the movie, the interview with the producers and Miyano Mamoru confirmed that they made this one with a western audience in mind. It's why we got to see it before Japan did. While that makes me happy to hear (that they care about their fans worldwide), the final product left me wondering what kind of view they have of western viewers. If this kind of thing is what they think plays to our tastes, then I'd prefer they just keep us as a secondary or ancillary audience.