Perhaps one of the most vastly overrated series of all time.
This is not to say that it is bad. It has good-to-decent character designs, fairly interesting characters, and when motivated the artist is quite capable. But it also has glaring flaws that force it into mediocrity: massive inconsistencies in the art (which will occasionally look like he inked his storyboards and submitted them as finished work), weak story-telling, and awful pacing.
Its initial flaw is that it fails to properly explain what a 'hunter' is and does. We are told what it takes to become one, and some examples of jobs that they do, but not why what the purpose of the Hunter system is, who authorizes it, who funds it, why they're in such high demand, or why it's so godawful hard to become one. There is no sense of coherency to the concept of a 'hunter'. This makes it rather hard to care about whether Gon passes the exam to become one.
The first two arcs, comprising almost a hundred chapters, are nothing more than a shallow excuse for fight scenes, filled with threats of an entirely artificial nature. The danger is real, but the danger can also be walked away from at any time. There would be absolutely no consequences if Gon and Killua walked away from the exam, and from there the story catapults directly into a rather dull tournament arc with absolutely nothing on the line. It is difficult to maintain tension under these circumstances.
Even once it moves past this phase, it runs into another problem: training sequences. Endless, mindless training sequences. The entirety of the Greed Island arc is, more or less, Gon and Killua doing training sequences while guys nobody cares about muck around with game mechanics in the background. That's fifty chapters, flushed down the toilet. This is not even including the chapters devoted to lengthy explanations of the mechanics of the pointlessly complex Nen system. The series is constantly interrupting plot for this sort of arbitrary garbage.
And the fight scenes just are not that great. Not bad, but extremely typical of a shonen series.
Overall, not a bad series. But it does not even remotely live up to the hype.
Except for Netero. Netero is everything promised and more.
[EDIT] As of the most recent chapters, the author has officially gone insane. Manga is now utter shit.