Spoilers for the manga

First off, I don't care how much you like Demon Slayer, that's your deal, not mine. Also, popularity doesn't equal quality, and it definitely doesn't in Demon Slayer's case. Literally all the hype comes from it's anime adaptation which is arguably better than the manga, but that's it. The manga itself didn't even come close to the following the anime got upon release. Ufotable really did a great job with the anime but that doesn't change the fact of how dogshit Demon Slayer is.

Let's start with the characters, specifically the main cast. Tanjiro as a main character is horribly written, because he's basically the "good guy" character trope that a bunch of other series use (think Dragon Ball or Naruto) but this time the author has to specifically point out that he's "so kind" because he's devoid of any other personality. All of his fights are an absolute bore to watch because "he doesn't like hurting people" and then remembers "oh shit I gotta heal Nezuko" and then proceeds to wipe the floor with whichever Demon he's fighting. Speaking of Nezuko, she's a terribly written character, and I can't even say "written" because she doesn't say a single thing for 99% of the manga. All she does is act cute, basically the pet dog of the show. This wouldn't be a problem if she was some minor character, but Nezuko being a demon is the center of Tanjiro's motivation for the entire goddamn show and it doesn't sit right that she doesn't do a single thing besides act as a crutch for Tanjiro in his fight's or be comedic relief. Going back to Tanjiro, he has NO character development, at all, and he's the main protagonist of the series. Like hell, he spent 2 years training and has nothing to show for it besides being able to cut a big rock. The point is, he doesn't change at all throughout the entire series and it makes you feel like you're watching the same static character over and over again.

The side characters are all badly written as well, with Zenitsu literally being a walking trope as all he does is act like a coward for the entire show until his master dies and then he becomes a badass? Neat character development. Inosuke is also equally bad as he's just the "strong guy who likes to fight strong things" character that appears in most other shonens. Unlike Inosuke and Zenitsu, the Hashiras are all relatively well written compared to them, as unlike them they have an actual background and motivation, so can't really complain about that.

Now let's talk about the Demons. Since they're the main antagonistic force of the show, you would usually expect for there to be more depth or something with them, but there's none of that. Almost each and every Demon is written to be killed off in the same arc they show up in, and they receive no development and have basically no character depth. All they get is a sob-story of a backstory whenever they're about to die to give them some "depth". However, the biggest pile of dogshit in Demon Slayer is the main antagonist himsnelf, anime Michael Jackson, the one and only Muzan, who is so utterly shit he makes me wanna kill myself everytime he's on screen. He has nothing to show other than being a douchebag bad guy all the time, and he gets no character development. Normally an antagonist doesn't need great development as long as they have some kind of depth, but no, Muzan has none of that, he just exists to be bad, and then eventually gets killed.

On to the main plot itself, it's just a badly done revenge story. That's it. That's the entire series summarized in one sentence. The show just follows Tanjiro and the gang going around killing Demons, and applies the same formula to each arc, just with a different setting and a different side character that appears to help them. That's the entire series, there's no switching things up or anything, that's it.

The anime did a phenomenal job recreating the fight scenes and adapting the manga content, and the sakuga was also great, but that doesn't mean much if I'm literally falling asleep watching the show. The manga had ok-ish art, basically what you would expect from a weekly series, but the fight scenes in the manga were sub-par. They were a lot messier in the manga and you couldn't really tell what's going on with the paneling, but that's a me problem. Anyways, I think Demon Slayer is a 2/10 for reasons stated above, and it's overall a really shallow, shitty, series.