Shonen adventure series, Hunter X Hunter's fame in Anglophone circles is scuppered by 2 things. Firstly it hit the airwaves in 1999 and ran to 2001, missing the bittorrent fansub boom that allowed the likes of Naruto and Bleach to explode. Weekly shonen shows work much better when viewed as intended, in weekly installments, and the bittorrent culture that emerged allowed this to happen rather than the trading culture of fansubs of yore.
Secondly the shonen shows that have caught on have also had the support of their manga, both officially and pirated. Hunter X Hunter on the other hand has had a patchy release schedule for the last 4 years, with the series now on permanent hiatus since creator Yoshihiro Togashi (creator of Yu Yu Hakusho and the husband of Sailor Moon creator Nakao Takeuchi) went on sick leave mid-2006.
The story concerns itself with the adventures of Gon Freaks, a young hunter in search of his father. Along the way he picks up numerous companions as is the way with these things. I've only seen the first couple of episodes so that's about all I know. Wikipedia tells me theres 62 episodes, it's toned down from the manga, there's OAVs continuing it. There's a bunch of musicals and a play.
I don't know, just watch the thing, the whole shebang is available fansubbed. Including the OAVs.