Up until Chapter 137, I was having a great time. Characters were fun and enjoyable, the Twelve Kizuki seemed creepy, Tanjiro trying to save his sister was engaging to read, it was paced well, really enjoyed it. The combat doesn't really stand out for the most part, but fights like Natagumo Mountain, Entertainment District and Swordsmith Village were all highlights and tons of fun to read.

However, in Chapter 137, after Nezuko survives the sunlight, Muzan leaves his fortress and directly confronts Kagaya at the mansion. From this point onward, the rest of the story is the final arc. Just for reference, all the arcs with the main trio up to this point were anywhere from 15 chapters at the least, 29 chapters at most. The last arc is 68 chapters long in total. That's around 1/3 of the entire manga spent on the ending. This absolutely destroys the pacing. Up to this point, each of the Twelve Kizuki would have their own unique fight against some combination of the main trio with one or two Hashiras that showcased their strengths, their personalities, and was generally really enjoyable. Now, all of the protagonists fight the 5 remaining Upper Ranked demons + Muzan, back to back to back to back, etc.

While the fights themselves weren't bad and a lot of plot points do resolve well during this, I just feel like it really took away from the Upper Ranked demon's importance since they were all shoved in the same arc. I understand having a gauntlet of sorts before finally reaching the big bad, but we had already began fighting Muzan before he escaped and dragged the protagonists into the Infinity Castle with the rest of the demons. Characters like Douma and Kokushibo were briefly teased beforehand, but they still didn't hold a lot of weight in the story until their fights, when we're explicitly told about their importance. Akaza's fight, however, felt extremely earned with lots of payoff, since we already saw Tanjiro swear to have his revenge on him after getting outclassed and killing Rengoku. There was that organic motivation already set up and it worked really well. The other demons unfortunately didn't get that amount of screen time. I'm content with Kokushibo being saved for the last fight before Muzan, but I would've liked Douma a lot more than I already do if we saw him being a dick to the main cast beforehand.

I actually really enjoyed the last fight against Muzan in the city. My only issues are that instead of the combination of him trying to save himself with the giant baby and putting his essence into Tanjiro, just having the latter when the sun was coming up would've made for a much more satisfying and tight ending since it was already going on long enough.

Overall, it's still a pretty great standard fantasy shonen that unfortunately suffers from a bit of a faulty final act.