They abaonded sprites in favour of dull coloured and expressionless 3d models. The pokemon sprites in Gen 5 was perfection IMO and they should've stuck with it in perpetuity.
Mega evolutions and Z crystals are terrible for game balance, and are currently ruining every tier of play except for the cool and varied PU tier. But Z crystals are even worse in PU actually.
Nothing has ever topped the gen 1 storyline, and the anime-tier fanfic they have nowadays insults the player's intelligence.
Gen 2 and 5 UU are the best and most fair competitive formats, and will remain so judging by the course the series has taken in the past few years