I was thinking of this manga this morning, and felt like I had to write these thoughts somewhere...
This manga started out so nitty-gritty, a slap to the face and very sincere. It worked with its motifs, and it established its reality pretty well as a solemn manga.
And then, arc after arc, it became more and more like a worse instance of Madeka-box, which means it went more and more shounen. So shounen, in fact, that shit made less and less sense, in favor of metaphors like "power of friendship", "the power of the hero" and all that crap. The rules of reality were literally bent and turn apart, just because a fight-scene needed a "metaphor". It became unreadable.
Imagine a story that goes in length to establish that its physics and rules exist in reality, and then someone leaps across buildings and sticks to walls. Why? Because "the character feels that way". This is how this story went to shit for me.
In short, this story started out relatively Seinen, and then fully embraced itself as the embodiment of Shounen manga. Sadly, this is no Claymore. <_<