I've been enjoying the series throughout as it been coming out, can't say I understand what fuss y'all been raising about. And from the comments I've read, y'all don't seem to really understand what part you hate about the series either?

I'm not even being snarky, I'm genuinely confused.
Man, there's no denying that this series had a lot of potential, a lot indeed. The art is good, the action is good, the comedy is good, although some people don't like the silly way it's written, I personally think it's good.
The problem is that the series has the poorest of the worldbuilding possible everything seems pointless - there was the Kaiju attack on the base, the one that turned into the vice-captain's armor, which theoretically would set a precedent for the story of the squadmate who is the son of the weapons manufacturer who supplies the army, which didn't happen, a waste in my opinion.
After that — there was the "death" of Kikoru's father — we witnessed a mini arc focused on the exhaustive training that Kafika and his companions went through, and everything else, with captains who were never seen again, except for one who happens to be the strongest captain of all and who "welcomed" the protagonist and Kikoru to his squad, even if we never heard of him before all this, still, that's the least of the problems we can accept he just happens to be the strongest.
The thing is that none of this really mattered, Iharu Furuhashi, a character you might not even remember exists, had a unique potential that only an absurdly strong captain of some squadron we never see again has, wasnt developed - while Reno, his rival, had unique training and managed to master a special weapon, it all felt rushed since we don't even see any of them in action before the climax of the manga, which makes it seem like the whole training plot, in the end, was irrelevant to most of the squadron. Therefore, the growth was not organic, it was forced and, in the end, useless and wasted - with the exception of Kikoru - not even Ichikawa mattered.
Then it gets to the end, and damn, Kikoru's father is alive 😲, because yes he is, Furuhashi's ability doesn't matter at all, because we don't even get to see him in action, the soldier boy, the rich boy, the girls, they dont matter and everything about them is wasted - even Ichikawa with all that talk about defending his senpai just to appear out of nowhere and have crumbs of prominence, so people remember that he is an existing character, not to mention that Samurai thing, which was poorly implemented - wasted -, Kafka relived the memory of a Samurai, because yes, he did, and, suddenly, the whole mystery got elucidated, it was just a random samurai who appeared out of nowhere to talk about something that, if it had been done well, would have been interesting, but that didn't matter at all, because we didnt need to know samurais fought kaijus in the past. I talked about this other things because i dont really want to focus on this last fight that is draging on for so long, since its near the end and it was, honestly, something i saw coming since this mangá only has 1 main villian.
Overall, Kaiju 8 is a work that had potential, but was so poorly scripted that in the end it seemed like 80% of it was worthless and pointless.
This does not determine the future of Naoya Matsumoto's career tho, he has the potential to be a great mangaka, but this work, unfortunately, fell far short of what it could have been.