-Spoilers-
Even putting aside the things fans have complained about the most-- the lack of monster battles, the questionable kaiju designs, or the inconsistent animation, City on the Edge of Battle fails for one overarching reason:
It wants to be a character-driven dramatic tragedy without any interesting characters, drama, or tragedy. This script puts so much stock and screen time into characters that it doesn’t take the time to meaningfully flesh out, and the payoff always suffers as a result.
Every character that doesn’t have a cardboard personality is an overused archetype that’s been done better in other anime, character dramas, or even other Godzilla movies.
One of the worst things a movie can do is kill off a majority of its cast and still make the audience feel apathetic towards it. Especially if it sets up an entire subplot to do so.
Yuko’s “death”, which is supposed to be the main emotional hit of the movie could’ve actually been tragic if she’d just been written better as a character. That kind of ending to her and Haruo’s romance could’ve been great if their romance had been developed beyond a handful of lines and kissing. The conflict between the humans and the Bilusaludo could’ve been interesting if it wasn’t so one-sided.
The worst part is that conceptually, these elements in the script *can* work, Urobuchi’s proven in his previous works that they can. The problem is they’re executed so poorly here, when they could’ve been so much better.
And that ending? It's an actual feat to sequel-bait with Ghidorah and somehow make that concept in itself not exciting.
The whole nihilistic feel the movie goes for is kinda fitting, in a cosmically ironic way. Nothing this movie does matters in the context of its own story. Anything with consequence feels pointless. Watching this movie and the trilogy it's from? Also pointless.