I hated greed island the first time through (well as much as I hate anything in hxh which is admittedly not that much) but I find myself liking it a lot on repeat viewings/readings. The dodgeball is probably the peak yeah, esp as it's a weird detour into sports anime during what is mostly until that point a training arc, but I like a lot of other stuff about it to. I like Bisky a lot so she's golden, the stuff with the cards whilst initially overwhelming and seemingly pointless (esp. in the anime when you can't read them) comes to a nice conclusion at the end during the plot to get Genthru and the payoff of that list bit as great, as Gon, Killua and Bisky all get cool moments.
Genthru is probably the weakest part of the whole thing as he's basically just a sociopath/psychopath. I think he extra stands out for this as most of the other antagonist characters in HxH are really memorable, which strong personality or motivations. Genthru is against our boys because he's a psycho, wants the prize and they're trapped in the game with him, rather than any complex reason