Apparently the author got a very large good feedback about the ending, or at least, he told so in the afterword (I wonder from which people, probably japanese audience, they always seem to like their own stuff in a different way from the rest of the world :D), thus decided to not write any more chapters of the ending.
After that he wrote chapter 53, long as hell, with an useless side story.
Those 50 pages of chapter 53 could've been, instead, 2 chapters for a proper ending, instead of a written essay on an afterword.
Wasted potential.
8/10 for the series, cut out ending so I'll give this manga a 7/10.