I love the concept and the fact that the main character is on the 'wrong side' and all the psychological exploration that comes of that. The art is solid, the author is not afraid to widen his cast, so the society feels real, which I like.
The problems:
-Too narrowly focused on particular sub-plots and loses it's synthesis as a story on the whole. He has great ideas, but executes them one at a time: first it's the his adaption and how that effects relationships with his old/new friends, then it's the new people he meets around him when learning his new lifestyle, then it's the government encroachment, then it's back to another plot on ghoul society, then back to another government plot, etc, and the mangaka sort of forgets the other stories while he's doing another, so you'll have a whole volume of one plot, then a whole volume of another, so it's really strange when suddenly he sees this 'best friend' of his again after 3 volumes and then doesn't see him anymore after that...
-Shounen style hero: As I mentioned at the beginning, there are great characters, the problem is, they sort of flip on themselves, so the enemy becomes the good little sidekick, all his psychological problems blown away by being beaten up by the main character (this happens a lot). The main character also had a lot of interesting concerns and personality traits that just get thrown away for him to be badass... which is momentarily exciting, but it destroys the development and long term coherence...
-Shounen style bad guys- I guess this goes hand in hand with the previous two problems, but the really important bad guy in one plot is removed, introduce new really bad guy, remove, etc and the whole story revolves around the bad guys, which sort of makes it boring after a couple arcs...
So, great manga, definitely worth reading, just no reread value and probably will go onto your unfinished list, so don't read it if you want to finish the series ^_^; (note that I am the kind of guy who got bored of naruto and bleach and noblesse etc etc so if you can continue reading those series for evermore, then this is perfect for you too)