There are few things they could have done with Mountain of Madness. It did not take into account 7-8 player games, the focus tokens do not have a +2 on backside so you would be short on those. Mystery where you have to do gates on Antarctica board there is one less then what would be needed, I guess have to use Advancing Mystery cards to get last one.
Also the unique asset characters should have done something with their backs instead of just duplicating, you miss out on a big chance to add more mixture to the game. They could done prelude card to just use backs of unique assets giving the cards different stats and actions.
They should have added extra two mysteries for each ancient one, since it unlikely see an expansion for those ancient ones again.