I've just got as far as I can in Hunter X Hunter and it's very good. The atmosphere is quite tense, I genuinely have very little idea of who will make it out alive. Their development of the two lead characters is very well done. In particular, the main character seems a lot like what I think George Lucas must have thought Anakin Skywalker's character arc made him - it's well-established that he's a good guy, even a likeable character, but he's got a very scary and vengeful side that actually stems from what makes him admirable in the first place. The other lead seems to have already undergone his development with regards to his primary flaw, but he's still interesting in how he reacts to the lead. The villains are also excellent in this arc, having developed in an interesting fashion on their own. So too the fights are enjoyably complex.