I'm sure it's been discussed to death in these threads, but damn I reread some chapters from Part 1 and early Part 2 and compared them to current chapters and I really bemoan how much the art quality has degraded
Fire devil has a cool design but he looks like a jumble of lines in most panels he's in
I feel like the decline started around chapter 135-150 and hasn't really gotten back to where it once was - you'll occasionally get some cool spreads but nothing has wowed me in a very long time.
Pic rel is probably still the worst panel in the whole manga imo