I, personally, have watched it 2x, which is a feat, considering that its almost 100 episodes =/
Plot: Dude in some world (alternate dimension) discovers that his dad is the greatest Hunter ever and sets out to find his pop. Even though he is searching for his dad, his dad never once appear. What this is interesting is the amazing world that they leave in, where every day is an adventure, really.
Add to that Nen ability and a complexed system guarding it and commanding its use, you get an AMAZINGLY real story.
10 points for plot
Music: Not much music to speak of. Or, I was too engrossed in the story that I couldn't notice the music?
Graphics: This anime excels by its story, not its graphics, unlike animes like Karas and Zegapain. Besides, this was made wayyyy back.
However, the action in the anime is amazing. Why? Because it is fast-paced and what they do makes sense, not some random superpower discovered after believing in oneself =.=
Overall: You would curse the mangaka for not continuing with this amazing story. Watch this anime or read the manga if you want to dream about Nen and Nen monsters everyday ^^
Rating for this anime? 8.5 (which is very humble)
