the energy system, it is almost impossible not to periodically end energy and have to grind at inns to continue playing as everything needs energy in the game.
In comparison in PoGO if you finish one category of scarce items you still have many part of the game you can play in (e.g. with no pokéball you can still fight in gym and raids)
But on this I am very critical of how Niantic is handling both Pokemon GO and wizard Unite