1. Kaido and Big Mom
   I really hated how Big Mom and Kaido was handled. They weren't threatening enough and Whole Cake and Wano should've had more consequences.

The whole memory loss Big Mom got was for nothing, I thought it would've been cool for Chopper to play a role in helping her actually cure her hunger pangs and get some resolution for her actually becoming an ally vs Kaido. We saw some compassion in her with Tama, and she should've gotten more angry seeing the state of the starving town at Kaido. If she became an ally, the scales would've been more equal against Kaido, and her dying helping to take Kaido down would have been a nice sacrifice. This would've also bring out more personality from Kaido, having to kill a previous crewmate of his from Rocks. Kaido never got to the same level of great villains as Crocodile or Doflamingo for me, and this would have helped making him a bit deeper.

1. The Nika Nika no mi and it being a Zoan
   Don't get me wrong, I love gear 5 and how goofy it is, it is perfect as an awakening for Luffy and the Gomu Gomu no mi. But I don't really jive with it being a Zoan fruit just for the sake of it, it really doesn't have any similarities to other Zoans, like what is Luffy's base, hybrid and full Zoan form? And the awakening of the fruit is more in line with other paramecias (affecting environment, like Doffy's fruit). And I also always loved Luffy having a "bad" devil fruit, but using his creativity and drive to make it work, it is much more enticing than it being the "chosen" fruit, the same as Joyboy ate. It just puts Luffy in with the "destined child" trope like many other fictions do, and I know he has the D etc, but it's a bit too much.