The story is very good, especially when it comes to the main plot concerning the 2 protagonists and their past. There is suspense and as you get closer to the end you'll have already gotten pretty invested in those characters (the two main ones, that is) so the climax is all the more intense. My main complaint with the story would be the filler chapters. There's quite a lot of it, and in pivotal moments too. For example, I remember reaching a cliffhanger at some point and after that the next couple of chapters were focusing on some totally random sidekicks that totally killed the momentum. By the time it got back to the main story my enthusiasm had died down again.
That's also my other complaint with Switch, the characters. There's too many side-characters, a few of them important to the story, but the majority of them are just there. You just get introduced to them in a chapter with just essential info about them and before you actually learn more about them they're out again. I found it hard to care about any of them, besides the two main characters and a couple of characters that were involved to their past.
Then again, I might have been more interested in the side-characters if I could actually tell them apart from each other! This is Switch's weak point for me, the art. Besides a few woman characters (who are actually, *very* few) who you can easily recognize, pretty much every male character corresponds to one of 3 or 4 at most different character designs. That cop with his little beard would probably be the most easy to recognize, because of the beard exactly; he had a distinctive feature.
The art in general is a mess. It looks very rough, as in "a rough, incomplete sketch". It looks "dirty", and not in an intentional way, not as if it's there to invoke a certain atmosphere. The good thing is that around chapter 30 it all gets better, the designs are much cleaner and with more depth. Until you reach that chapter though, you'll have to brace yourselves...
I could have even let the filler arcs slide if it weren't for the bad art. If there was something that ruined my enjoyment of the manga was that alone. I had watched the OVA first and then read a couple of chapters and I was pretty hooked on the main characters alone (Etō Kai more specifically) so I didn't really want to drop this. But I found myself struggling to continue. I actually pressured myself to keep reading sometimes. Like I said, around chapter 30 it all got easier with the improvement in the art. After that, it was pretty enjoyable, I have to say.
My recommendation would be to check a few pages of some of the first chapters without reading anything, just to check the art. Then do the same for some pages of chapter 30 or later to see the difference. If the art is something you can live with, then the story is definitely worth it. But if the art is displeasing to your eye, maybe you shouldn't try this at all. If I hadn't watched the OVA (which had great art, of course) and liked the story already, I would have dropped this very quickly.
