I started in gen 1 and have objectively played every game since at release, so my opinion on all games is the correct one:
XY are good, but were the first games to really show the cracks and limitations of game freak. The first two thirds of the game are very fun, but after that it sort of falls off a cliff. About two thirds of the way in, the story just sort of ends and then you just wrap up getting the last few gyms and league without anything happening. There's no postgame either. It's very evident the game was unfinished due to being the first 3d game they made. It would be excusable if they made Z, but for some reason they didn't and that drags down XY a lot. I still don't understand why they didn't give the games a proper 3rd version or sequel, it's still the only gen to not have one. Overall, the game is fun, although the region is smaller and there's much less to explore than the previous generation. It's the worst of the first 6 generations, but is far better than the games that have come after it.
