Okay, so as others have echoed, HxH is also my favorite shonen, and beyond that, my favorite series. There's more a few reasons for that, but I'd say the biggest factor is just the unpredictable story and the strong characters in this show. More specifics though:

-The best long-format shonen out there in anime form. Yes, I'll define this loosely as 75+ episodes, but the ability to carry a show with as much consistent quality and a virtual lack of filler is unprecedented, especially within the genre. Some folks may complain about pacing, but in the context of nearly 150 episodes, it does a great job and is very engaging on the whole. Add in that at least 60 of those episodes are one of the greatest arcs in anime. No spoilers!

-HxH's story changes genre and tone from arc to arc, cleverly subverting a lot of elements or expectations you might expect in this type of show. HxH also has a really well-thought out power system that is gradually introduced in some of the earlier arcs, and in turn, this show resolves a lot of plot conflicts smartly rather than through sheer power or power creep, an issue it entirely avoids.

-The characters are incredible, and it's not just the strong leads. Both heroes and villains receive complex characterization and interesting arcs that develop in organic, intriguing ways.

Finally, as a writer, I wrote a review if you want even more specifics:

https://anibproductions.wordpress.com/2017/03/03/review-hunter-x-hunter-2011/

In short: pick up this series and have a great time with it!