First half of the movie is slow, standard recap of the heroes backstory which is a bit redundant considering how often the show itself keeps reminding us.
The fights are fairly poor for a film, sadly outdone by other lesser budget TV series by the same studio (mob psycho, darker than black, full metal etc). Enemy is a generic (will create a new world) villain and the overall story is a pretty typical episode of the series.
It picks up towards the last twenty minutes where the animation gets a little better but it's towards the very final fight scene where it feels like a movie.
The animation gets crazy and epic, combined with the one thing the my hero series gets done right (the "feels") and you're left with a satisfying feeling at the end.