Hunter × Hunter is a rather underrated action/adventure/fantasy anime (based on a manga) that I have just finished watching in its entirety. While the general premise of the story is not anything terribly creative, the fantasy elements of the story, especially Nen, are very imaginative and interesting.
The storyline revolves around Gon Freecss, a boy of twelve, who finds out by a chance encounter, that he really is not an orphan as he once believed, and that he is actually the son of Ging Freecss, purportedly the greatest Hunter in the whole world. This drives him to become a Hunter himself in order to find his father and ask him .. WTF? or something similar. In the course of all all this, Gon makes interesting friends and powerful enemies and generally embarks on adventure upon adventure.
The direction is, IMO, rather dodgy, and the storyline does not exactly overwhelm you with its complexity or ingenuity. However, the characters are likeable and as mentioned above, the imagination element is excellent. If you are into such things, this is definitely worth the watch.