I always struggled with Rotation battles because of how frustratingly unpredictable they are. One Pokemon is weak to my starter, I rotate my starter up front, but the opponent rotates to a Pokemon that resists it, so my starter takes some super-effective damage it didn't need to, I swap out to something that can counter this second Pokemon, only for the first one to rotate back around! The whole thing is too much of a pain and I hope it never returns, but by comparison Triple battles were fairly straightforward because you can simply adjust your team to face whichever of the opponent's three Pokemon they counter the best.
To the contrary, I think they were entirely about prediction. In that scenario, it sounds like your opponents were able to outguess you at every turn. There were all these Japanese players I encountered who could do exactly that, but at the same time, I learned a lot about Rotation Battle thinking playing against them. You also can't put in a team meant for single battling and expect to win against a team made specifically for Rotation Battles. Namely, Protect is just as important a move in Rotations as they are in Doubles, but you have to consider that the Protect/Detect/Endure counter is separate for all three of your Pokémon on the field, meaning youcan use it on consecutive turns on consecutive Pokémon but at the cost of being locked out of using it on consecutive turns.
Also, the AI is a dirty rotten cheater in Rotation Battles.
I would like to see the return of Mega evolutions or turn those forms into a permanent evolution for those Pokemon. Balancing as they go as they would probably be overpowered to be a permanent evolution with their original boost.
The deal with Mega Evolutions is that the Mega Stone already occupies the item slot, so they're balanced out by not being able to hold any other item. Allowing a Mega Pokémon to hold an item is what put Mega Rayquaza into Anything Goes.
I don’t know if this qualifies as a feature, but I think Normal-type Pokémon should receive a x1.75% STAB to their Normal-type moves in Gen 8. Normal has no advantages offensively (outside of coverage in specific circumstances), so a 25% bump would help the disparity between normal offense and other types. Normal still has the defensive advantage with one weakness and one immunity. So, true to their nature, a slight boost to offense would help keep them well rounded.
I just want to see this type do as well as it did in the first Gen, but that may be a pipe dream with so much competition.
Normal-type attacks are resisted by so few Pokémon that they're reliable general-use moves, at least when put onto Normal-type Pokémon. For these reasons, I think they're fine the way they are.
Well, there's also the fact that the Normal-type exists in the games as both the control and as a way for beginners to ease into the battling system (though this has been slightly undermined in games where Fighting-types get introduced earlier). It's also an early-game crutch type, since a lot of games throw Rock-type trainers early on, who are there to force you to diversify your team. If the Normal-type needs a power boost, I think it should be via an item, like the Normal Gem, to allow for greater customization and to not make the early-game Pokémon too powerful.