I feel like the movie just didn't quite do it for me.
It's a shame because it got off to quite a good start, it just didn't go where I thought it would or where I wanted it to go and it left the ending feeling a little hollow.
The art was okay, standards are lower since it's an anime obviously, but for the most part, it didn't intrude on the enjoyment of the show so I guess it'll pass. The animation was also nothing exceptional for about 99% of the film, so that could have also been part of the reason the characters felt less interesting.
I don't believe sound to be a massive factor, but it was very good here, I liked the song that played while the credits rolled.