I read the last chapter right now, so I'm writing with the freshest impressions that I have. So take a big BREATH and let the DANCE begin.

Note: I didn't watch the Anime and as I read a lot of people are influenced by it. And what I saw in trailers it was really well animated, so there is a chance that the Anime is better than the manga. But my review is completly untouched of the Anime.

Story 7/10
The Story begins really intresting, but soon you experience the may lack of this serie, the pacing. After the beginning it's skippinng "unnecessary" things, like a long training session. First you may think: "oh yeah, we don't need this boring stuff" (I'm also one of these) however this also results that in just very few chapters our protagonist is on the same level or higher than other demon slayers (just from hitting a rock and running in the forest...). And this "skips" happen after every big fight. You get 1-2 "training" chapters and of course the time passes, so it's not just 2 days or so, sometimes it's weeks or months, but first he fights some low level Demon and just after that it fights a top tier demon... Also the final boss appears almost at the beginning, which give us a clear direction for the story, but at the same time it takes important / intressting side stories. You won't get to know the characters or the world very well because you have to rush to the next big enemy. At the end, you just run from one big fight to another.
I'm currently swaying between 6 and 7, and now I give a 7. That's because you maybe rush, and maybe you don't get enogh explanations (worldbuilding, how the "powers" work etc.), but if you don't need every detail in them (like me), you will get a fast and intresting action story.

Art 6/10
Oh boy... I'm really not a fan of his style... Not at all. For me, it's poor drawn, sorry. The lines are shaky, sometimes it's missing things or changes in a even more poor style... Especially for the action scene it's really a downer... However! It is special, fresh and individual. It also gives a touch of comedy (what doesn't work everytime, but I admit, I smiled sometimes). So I can understand why somebody like his style, and I try to be as neutral as I can. Also, if I get a good story and/or action, than I don't really care if it's poor drawn or not (but I had to get used to it...).

Character 4/10
As I mentioned it at the "Story" part, due its pacing, you won't learn a lot about the characters. Sometimes they just come and go, why death is permanent and nothing special in this story (maybe shocking at first, but after the 3rd or 5th you just say "meh, another one"). Even the "main" support characters are really poor and mostly just annoying, while the protagonist is just a mediocre shounen hero. The only good point about the characters are, that you get a lot of individuals with different powers and reasons for fight. So somewhere in this story, maybe your dream character is also in the story (but don't get to attached to it ;) ).

Enjoyment 8/10
Yeah I know, it don't have a deep story or characters. Also the Art isn't in my favor, but I really enjoyed the Action (even if it was sometimes longer than needed, for example the final) and I mostly also liked the fast pacing. So if you are shounen action fan, you will get what you expect.

Overall 7/10
You won't get the best written or drawn manga of your life and the last 2-3 chapters will, with high a chance, disappoint you, but if you like a fast paced action shounen (kinda like Dragon Ball Super) you will be satisfied. For me, with a better art or a deeper story it would have been at least a solid 8, but for now it's just a weak 7.