Now I wouldn't say that this is the best piece in the world, but damn is it one of my favorites. It's slow-paced, but not too slow. Only about 30% of this manga is fighting (if you can even call it that), which is unusual for a shounen. Honestly, this series is only shounen for the first part of the series, then it shifts into more of a seinen with shounen undertones.
This series really develops the characters through the story. The main character goes through some very notable changes. I mentioned earlier how this series shifts from shounen to more of a seinen; this shift is brought about actually by the changes in personality of the main character. I find it interesting how in the beginning of the series, the MC is super self-conscious and acts like a total shounen MC. But as the story progresses, MC slowly starts to disassociate with the world around him, turning him into more of a seinen character. It'll make sense when you read the story, I promise.
The main reason I love this series is because of the ART. I kid you not; I have paused during every single chapter to admire just how gorgeous the art is. Each expression is so clear and variant - you never see quite the same expression more than once. But man, the art is fantastic, and if this series is ever made into an anime, we have some GORGEOUS scenes to look forward to.
Basically, this series is a very fun read if you just want a good supernatural drama. I have enjoyed the hell out of it and am rereading it for the third time.