This was really painful to read. It starts as a comedy action manga but by the end it devolves into what are basically two different comics. One is a mostly serious fantasy/sci-fi manga, and the other are a few - and mostly canonical - gag comics at the end of each chapter. Reading the last few volumes feels like watching a movies on TV with a comercial break every 5 minutes. You just get into the story and then the story halts and you have to read this BS 2-6 pages gag minicomic. And this happens for almost every single chapter.
The story itself would probably be a 6-7, but the gag strips and minicomis just kill the mood on the regular. Either one would have been ok, but both combined, it just give you tonal whiplash.
Even then, I'd probably give this at least a 5 if not for the epilogue. And if you're wandering what's wrong with it, it's basically a LotR type of deal. I mean, on the one hand it does end a lot of story arcs, on the other, it keeps on going, and going, and going, and going. And no, I'm not exaggerating.
This isn't a bad story, but the supplemental gag material that can be found in the later volumes really shouldn't be there. One or two at the end of a volume are fine, but 1-6 pages at the end of every chapter really is too much.