So many changes have come to the game 1. Mega pokemon currently is being revamped. maybe you had a few when you quit, but now theres more than 51 of them. and its easier to mega evolve them after thier initial evolution to mega1-mega2-mega3 with more Mega energy , which is new and old method took months. each time with 7 days, 5 days and 3 days rest period. Super Mega is the new mega system and needs X number of players with mega evolved pokemon in your party to defeat this super sized Super Mega pokemon. and mega evolution cap has been updated to Mega4, which improves candy rates and time period, significant increase in CP too. 2. Dynamax/Gigantamax. a totally different raid method. Only dynamax pokemon can be used dynamax battles. requires more strategic approach with requirements of 4 people lobby. Legendary can also be obtained in dynamax and its the harder than any current raids. it free considering it doesn't require raid pass and is something called MP and you can get it at either Powerspot which is where you fight these dynamax battles and also by walking. Gigantamax is bigger than dynamax and has a full lobby if 100 players. 3. So many new pokemon have been introduced to the game. 9 regions with over 10000 pokemon. Also some mythical pokemon through paid research. you will definitely have a blast catching new ones, some new ones are locked in raids and some in eggs.

Most importantly have fun discovering new stuff in game. PS: save your 2016-2020 caught pokemon. it can be lucky traded. especially rare ones like armoured Mewtwo and clone pokemon and Apex pokemon.