HxH did everything right. It is a show that literally cannot be improved in my humble opinion (except for that non-ending ending). It's pacing is superb (It gets good faster than any long shonen series), it has no fillers, and even the worst arcs are still good. The story and the world Hunter develops is just really damn good, and the characters feel real. They have depth and are more than just one-dimensional shonen clones.
I suppose you could say the series lacks romance and isn't super big on the humor, but outside of that I don't know what else you can ask of an anime that Hunter doesn't provide. I keep my average rating of shows pretty low (6.5) so that a 9 or a 10 carry weight as a ranking. Let me assure you, HxH is a 10. It is a masterpiece.
