It was pretty good imo. Misty and Brock were very entertaining. Whole Misty and Lana scene(i knew they would get along great given how much they have in common haha).
Brock being impressed about Killie knowledge regarding pokemon seeming like he did not just improved in studying to be better doctor, but as trainer too.
Fact that while brief , scene of original trio alone and return of long time forgotten pokemon such as Squirtle, Muk etc added sense of this episode being like time machine to golden days of pokemon series liking how friendship between Ash and Misty, Brock remained just as strong like they never separated. Yet Ash friends grew in strong professionals being like teachers and mature instructor for everyone else involved in this school class on open.
Man Misty turned Cerulean gym in freaking stadion haha, hoping she will win that battle.XD
Everything breathed with not just nostalgia, but emotion and lot of charm intertwining this episode. However there is one flaw marking this episode and entire return of Misty and Brock in general. It is TOO SHORT sadly. Because while brief scene on their own were nice and enjoyable for me, they were too brief, too many characters fought for focus and i feel Brock and especially Misty after such long absence deserved more screentime and exposure.
Two episodes to cover everything and get more meaningful plot out of this arc just wasn't enough im afraid.
Maybe im greedy in wanting more, but after remembering how great Misty as character was and still is showing she knows how to light up show having lot more to discover about her, I don't want that she disappears in oblivion again.