After playing SM, I went back to replay Platinum.
I had always taken gyms for granted, but, holy shit, they're a slog compared to trials. It's not like gym puzzles are particularly fun or interesting--the solution is usually pretty obvious, and it just takes busywork to actually complete it. And your reward for that is...being underleveled when you face the gym leader. So you sometimes end up having to go through each step twice, once to fight the trainer and then a second time to advance.
Each trial at least had a bit of a narrative to it, which made them more immersive. Gyms, meanwhile, always felt like you had temporarily wandered into a game from a different genre for no adequately explained reason. Gyms also failed to really provide any sense of rising tension, since you could always backtrack to the Pokémon Center and then come back to where you were. Hell, you could walk up to the gym leader and then decide to jog back in order to heal up. Trials locked you in, and every step was a step forward.
I can't think of a single thing I miss about gyms.
