Review of K
I don't have any major criticisms for K. Nothing about it comes off as a dealbreaker or particularly obnoxious aspect. That said, it isn't without problems. The biggest one is that it has such a large, branching story and so many characters but it's still only thirteen episodes. Which makes the pacing feel overly fast and leaves some things less detailed than they could be. That of course hurts the characters a bit. There are a ton of characters in K, and none of them are especially well characterized. Partially because they all have to share the thirteen episodes of screentime, but also just because thisanime isn't great at fleshing them out. They mostly have only a few traits and aren't that complex. Even the ones we see more of like Shiro and Kurou.
I should point out that I don't think they're bad characters either. In fact, I like most of them. Their personalities are simple, but well defined. Almost everyone has a good balance of postive and negative characteristics, which I look for as a sign of good characters. They have sensible arcs if they have any, and their conflicts are compelling. Probably the strongest point of the anime story-wise. So let's call the cast alright on balance. I hate Neko though, and the villain is very one-dimensional.
Quite a lot of the time this show has is spent on character scenes. And most of the rest of it on fights. It has a high budget with very nice animation and the fight scenes are fun.
It's fun in general, is what I'm trying to get at. I'll freely admit that it isn't the deepest thing in the entire world, and the structure is flawed. But I do enjoy it a lot. It's silly, and it does a good job keeping the tone light. It doesn't handle anything particularly dark and the execution softens its content further. And like I said, I like almost all the characters. For me that's enough. It's always good to watch something just for fun now and again, and there are much worse written anime than this anyway.