Story: 7/10
The synopsis is quite inaccurate in describing the show, since it explains essentially only the first 4 or 5 episodes. The rest of the story is various sub-stories that sort of fit together, but can probably be told in isolation. The last arc is an exploration of our main protagonist's past, and how its consequences continue to haunt him. Sadly, the writer for the source light novels passed away before he could finish them, so you'll have to be okay with a cliffhanger ending that will likely never be completed.
In terms of storytelling strength, KnS has its weak and strong moments. At times, it seemed like the story took an easy road out with a simplified and partially unexplained resolution, but at other times it delivered on its build-up and presented a satisfactory conclusion. Since there are various arcs throughout the show, some of them are done much better than others. And if you are looking for a satisfactory ending, you will likely be disappointed due to the unresolved cliffhanger.
Art & Sound: 6/10
I try not to let the music or animation affect my opinions of a show, but I would have enjoyed the show a lot more if these departments were improved. I'm not sure if other 2007 shows were all of this quality, but because there are many fight scenes in the show, bad animation and music significantly affects those types of scenes.
Character: 6/10
To be honest, there isn't much character development. At the end, the characters are pretty much the same people they were at the beginning. There are changes here and there, but because the show is more of a shounen, the focus is on the action. If you're a fan of overpowered characters, however, KnS will suit your tastes, and is basically the only reason I kept watching. If you're looking for anything else in this department, you probably won't get it.
Enjoyment: 8/10
I watched and finished the show simply because it had a badass main character. In most other aspects, the show was very average, but not bad by any means. If you want something else, or something more than that, KnS is probably not for you.
Overall: 7/10
If you like badassery, give KnS a try, but I wouldn't blame you if you dropped it.
