I recently finished up the Demon Slayer manga. I definitely liked the first half more than the second half. The Hashira arc, wherein they go undercover in an entertainment district to find a demon, was the last arc I really enjoyed and probably also my favorite. Felt like the author, Koyohaur Gotoge, got bored or burnt out on the series during the swordsmith village arc and decided to rush to the end. Zenitsu and Inosuke feel like they become background characters, with Zenitsu's big, personal battle feeling like the author throwing him a bone after realizing he hadn't done much with him. Even Nezuko barely shows up during the last 50 or so chapters.
Well, at least there were still a ton of insane battles that ufotable will beautifully animate. I'm curious as to how long they plan on making the anime. At their current pace of roughly 2 chapters equaling an episode they have enough material for three more seasons but I can't see them letting it run for that long.
Also, one thing that kept striking me as odd was that author would make sure to have the characters use archaic measurements appropriate for the era but then would have them talk about cells, genetics, and diseases as if they had modern knowledge of them. It wasn't something that affected my enjoyment of the manga but just something constantly stuck out as weird.