This episode is an absolute roller coaster! We begin with Gon immediately thrust into a dilemma where he has to evaluate and prioritize the things he values the most: loyalty/friendship, and the pursuit of his father / the Hunter lifestyle. While not forced to make an immediate decision, getting to see him grapple with this choice is very compelling.
Gon's dynamic with Hisoka is the crux of this episode, and the writers and directors explore and illustrate every facet of it. The enigmatic joker figure is developed even further here, and every scene he appears in has a palpable energy and tension to it. His flamenco-inspired theme in the score is electric, and all of the additional ambient sounds perfectly augment the tone of each scene.
The other brilliant aspect of this episode is the symbolic significance of the hemotropic butterflies. They're used to represent bloodlust, foreshadow violence, and illustrate the dire situations that Gon finds himself in over the course of the episode. They were beautifully integrated into the story through subtle directing choices, and really made this episode stand out for me.
This is definitely the best episode of the series thus far, and it serves as a perfect setup for one of the best payoff fights in the history of anime in the next arc!