This was a fun, enjoyable, feel-good episode. I was hoping Misty would get more focus in this episode than Brock, since Brock gets to be the focus of the next episode, and I wasn't disappointed; the writers even wrote Brock out of the episode in a way that made perfect sense for his character (helping Nurse Joy at the Pokémon Center). I wish Misty had been more of a focal character, but her interactions with the SM cast were fun.
It was nice to see Mantine Surf in an actual episode, but I also appreciate the reference to the Eevee segments with the Mantine that Nagisa rode from the ship to Alola. The callback to Psyduck's inability to swim was humorous, along with Marowak being afraid of the water. And thank you, writers, for not resorting to slapstick comedy and having Ash wipe out while surfing!
It was nice to see everyone work together to defeat Team Rocket, but as much as I like seeing Z-Moves and Mega Evolution in action, that was complete overkill. They had pretty much already defeated Team Rocket.
I have to say, however, that the most heartwarming part of the episode was Brock setting up a tent and campfire and cooking a meal for Ash and Misty, just like old times. Kukui and Burnet watching them from the window just added to the moment.
My main complaint about this episode is Team Rocket's interference. It was just as cliché and predictable as ever. Sure, it was a true callback to the days of OS, but we have had to deal with twenty years of Team Rocket doing the same routine—building some kind of machine and kidnapping (or attempting to kidnap) Pokémon, only to blast off in the end. And they actually blasted off; Bewear didn't even save them. IMO, we don't need that kind of "nostalgia."
(On another note, I'm starting to wonder how the fruit seller makes any money if she keeps giving away her wares to Pokémon.)