One thing that really bothers me is the default camera angle that the camera shifts to when you have a Mega Diancie on your side.
It's almost a bird's eye view. Diancie just sits there at the bottom edge of the screen, barely visible.
Some mons seem to have a weird angle too. Rather than have the camera pull out, a lot of big mons just fill the screen (Mega Latios, Mega Altaria).