This is hands down, one of my favorite manga of all time.

Story: 10/10
Part of the why the story is good comes from how it is told, there's no worthless filler stuck anywhere, it's pure story all the time. The story is always moving forward, there's not even chapter breaks. There are also some spin off manga (two of which I have read, the ones that Viz published in the back of the last volumes) that tie coherently within the rest of the story and help explain a few things that are in the "nice to know" type category. Another thing I found important is that I could see where all the plot points evolved from, I never felt any sense of deus ex machina anywhere.

Character: 10/10
Characters are just as strong as the story, Ash isn't the only main character, even if he is the most interesting of the main characters. The characters all feel real and realized including the way that they interact. Even bit characters who only show up twice in the series are memorable (like The Fly).

Art: 6.5/10
Easily the weakest aspect of the series. The art is never unclear as to the action, it's just not the best thing ever basically. A lot of the characters have a similar facial structure and for quite a while, I confused two characters with very similar mustaches and hair styles/color. My complaints here are mostly minimal though, artwork does improve during the series and it never takes away from enjoyment factor either. But this is not a series you read because the pictures are pretty to be sure.

Overall: 10/10
I rarely give out 10s, but this series made me feel so attached to it that I actually cried at the end of it for several reasons. The addition of the two side stories that Viz decided to publish only helped the series out. I think this is a must for fans of drama with some action series if slight yaoi undertones don't bother you (that are never shown onscreen so to say). It's epic to say the least, it might be classified as Josei, but I think that this is just as much for the Seinen crowd too.