XY started some bad trends but I still really like it.
Mechanically it added a lot and I really like the changes it made, with Fairy type, electrics being immune to paralysis, etc. I know people are torn on Megas and I see why but I do like them I just wish they didnt replace actual cross-gen evolutions. I really like the Kalos region itself as far as map layout and theme goes too, and the Pokemon distribution is great. The online functionality was actually somewhat ok and is still the best it ever was in gen 6. It does make some huge mistakes, the small amount of new Pokemon blows, the games are way too fucking easy, and the intros are a bit too long. But 6 actually tried.

7 added nothing, actively replaced some of 6's positive changes with worse versions (Alola forms, Festival Plaza) and repeated every single one of its mistakes while adding more of its own.
tl;dr 6 is good. Far from the best but good. With a proper hard mode it might even be great. 7 is just a travesty.