The starters have a secret in that they're important to the plot, meaning that they'll be relegated to a few short insignificant cutscenes in the earlygame and soon dropped. You, however, will not be able to box your starter until you reach the equivalent of the Elite Four, since they're so important to the plot and all.

Pokemon don't actually have any more personality than in XY, those animations are just the "rare" animations that play while both players are waiting to pick their move. Pokemon battles will play out the same as in XY and ORAS: both combatants just standing there. The only thing that's changed is that the Trainers will emote when they get hit.

Speaking of Trainers in battle, the models will disappear when field-changing moves such as Surf, Earthquake, etc are performed. They will reappear immediately after the move is done.

The Aether Foundation will not be the villains. Team Skull will be a reskinned Team Rocket, only slightly more fleshed out. Guzma, Plumeria, and Gladion will go through a redemption arc.

The camera feature will be as unexplored as it was in XY. The majority of Pokemon you can photograph in the wild will be gen 1 Pokemon.

Mega Kangaskhan and Aegislash will be nerfed in some way. However, Game Freak will not touch anything else, believing those to be the only overpowered parts of the game.

Unlike Mega Evolution, where the special animation of the trainer holding up the Mega Bracelet will only play the first time and not even in battles, Z-Moves will force you to watch the cutscene every time.

Poke Ride will be unavailable in most of the game.

Alola will be extremely detailed, meaning the map and the game itself won't have much content and Game Freak will "remedy" this by prolonging the game with cutscenes and meaningless dialogue from your "friends".

You will be given a Rockruff after the first town. The NPC that gives you the Rockruff will go on about how the bond between you and that Rockruff is extraordinarily special.