Just starting this one but so far it's developing very nicely, story is quite good, not original but the humans as enemies twist is nice and Helcks story is interesting. Chars are great so far, Vamirio is the best, Helck is not only interesting but deeper than he seams and the rest ain't bad either. Even dialogues are good when it's not trying to be a comedy. And above all, at last humanity is the villain!! Many series depict humanity as viruses or cancer or whatever but almost always if not always, the author ends up siding with humanity nonetheless, so far this one is different, hats off.
It does has a few weak spots, mainly that the villains and their motivations are crap, also, as a side-note, that even when the art-style is great the fights are so-so, but in any case, the good heavily outweighs the bad, best of this type of mangas I've read in a while.
Even the omakes are interesting!! I usually just skip omakes in mangas, few have anything to do with the story and re usually quite dumb and fail to be funny, Helck's are funny and more often than not add to char development. Thou I have to say it's pretty annoying that there are more omakes than proper chapters, the story is being disrupted all the time... ended up skipping them and then reading them all together when the plot takes a breather.
Edit: also, the ending of the arc is terrible, it's ruining the manga... it's simply too much, it's no longer "believable".