Meg Evolution was cool but the reason it’s my least favorite is only a select amount of Pokémon could mega evolve
Z moves were a very nice addition, nothing crazy tho and plus they wasted an item slot
Dynamax/Gigantimax was a really neat concept. But..
Terastallizing is the best one yet imo. Every Pokémon can do it, you have a 18 choices of terastal that you can do for every Pokémon, it looks so cool, and it’s fricking powerful
Haven't formed an opinion yet on terastalization but here are my thoughts!
Megas were a refreshing mechanic added to Pokemon to add more depth into the already well-developed world. Not really insane for it but it's good, albeit unnecessary (and broken *cough* Kangaskhan and Mawile)
Z-Moves were nice and fun as well, feeling specific to Alola but they are infamous for ruining competitive by being op hailmerries
Dynamax is a nice concept but really boring. Better executed as a gameplay mechanic
Mega Evolution is epic. Gigantamax is kind of cool. Terra is meh maybe because I am displeased with the Gen 9 games since launch. I hope the anime based on it fixes it.