Where are you up to right now? Is it the east Antarctica arc? It did slow down a bit and the next arc is a slow burn but has a great conclusion (I can't say more without spoiling). In around 400 chapters, the story switches vibes to a more chill and relaxed portion of the story, and this is seen as the weakest part of shadow slave so far. Once again it's really hard to describe without spoiling but a summary would be: where you are to around 1200 is ok, the next 30 chapters after that are also a bit slow. Then something happens at around 1230, and the story really slows down till around chapter 1300. It picks up a bit until the conclusion of the arc at chapter 1550 to 1580, which is the climax of the next arc and it's a really good conclusion to it. Then from around chapter 1600 till 1800 it's a lot slower with some interesting parts, and then from chapter 1800 till 2200 the story begins to pick up again and there is a lot of action from 1800 to 2200. I hope I didn't spoil anything for you, and my memory might not be 100% correct but this is my rundown on how the rest of the chapters up until the latest goes. But even the low points like where you are at now are still really good, and you should just enjoy whatever you are reading now. The story doesn't necessarily get worse but there are some weaker parts and honestly it depends on what you like. I personally loved all of it and was hooked the whole time, so it's not bad at all. Like I said, enjoy it while you can because it's all really good.