To elaborate a little more behind the spoiler tag, there were a lot of parts heavily implying Gon's naivete, thoughtlessness etc. would lead him into something violent and morally questionable that Killua would be left bearing the brunt of. This never happens. There are multiple times when the stupid things he does either hobble him somehow (see the loss to Knuckle and Shoot, which I initially thought was going to lead him to disobey the hunter association and put Killua in danger too, or at least saddle Killua with so much guilt he'd leave the way he resolved to) or put other people in danger (everything to do with Neferpitou and Kite's death). However he never bears any real consequences for them beyond his role in Kite's death in the first place -- guilt over which he doesn't come to terms with until he actually learns Kite is dead and not just possessed. Even then it just goads him into tearing Neferpitou to shreds. The other main characters never meaningfully reckon with them either. The scene of him lashing out at Killua in the tower when he can't attack Neferpitou without killing Komugi in the process is heartbreaking, but it just...doesn't matter when after another few EPs he successfully guesses when he can pull Neferpitou away leaving Komugi alive, intimidates her into getting all the way to Kite, then kills her when he realizes she can't restore Kite, before Killua can get there (though I guess he likely would have died had Killua not been there to carry him back). I also don't have the faintest idea what Togashi was thinking with his "transformation" in that scene -- it's the most anticlimactic garbage. See also the fight with the chimera ant "king" (whose introduction made the show infinitely more boring to me in the first place but that's a story for another day) -- in the end, it's just the bomb Netero sets off at his death that kills him, and none of the motivation for even having Nen users deal with this stuff is clear anymore. There are paragraphs more I could say on this, which I guess means Togashi was doing something right at some point, but...
Final thing I want to mention since I don't seem to be able to leave this alone is that the chimera ant nest itself was sidelined way too fast. A claustrophic, maze-like setting like that would have worked well for the kind of thing I'm describing between Gon and Killua -- it's a tense, dangerous environment, it's hard to leave, it's somewhere easy to make mistakes... As far as I remember, they never even get to see inside before the king is born and the entire "ant hierarchy" gets invalidated, everybody scatters to the four corners of the earth, and the king sets himself up in an existing human palace somewhere else (and does pretty much nothing but play boardgames against Komugi for the rest of the show). His guards are terrible characters -- Neferpitou is the only one who's not an outsized caricature, and she's still just not very interesting...
I guess Greed Island, while it didn't feel like much of an arc on its own, at least didn't do anything horrifically wrong. Even had a fair bit of the foreshading that Togashi seemingly didn't end up knowing what to do with -- horribly burning Killua's hands in the fight with Razor, Gon in probably the goriest state you ever see him by the end of the fight with the Bomber, etc...