>>46449927XY came out with massive improvements to the game's basic infrastructure. UI design is still among the best in the series, alongside HGSS. Having live multiplayer built into the touch screen + EV Training from anywhere in the game was a-lot more useful than the C-Gear. The fundamental draw of Pokemon to me is the monster collecting and Battling with friends. For all of its shortcomings, XY made that process into something that was actually fun and doable.
Gen 5 removed Berry farming for some reason, and pushed it to the Dream World (which is now inaccessible). XY brought it back with a dedicated garden where you could make your own mulch, and find rare berries on your own time.
Gen 5 introduced Hidden Abilities, but they were an absolute chore to obtain unless you were willing to spend hours on their browser game (which, again, is inaccessible today). The Friend Safari and other alternatives like the recent Ability Patch are much preferred.
Region design was incredibly rigid. You only ever go from one point on the map on to the next, and backtracking is discouraged. XY has linear progression, but Kalos radial map makes it kinda fun to go back and forth between cities through Lumiose as a "hub world".
The animated Sprites aren't great. Most of them are just recycled from Gen 4, and look heavily pixilated. If you want to see nice animated Pokemon sprites, the Pokemon Ranger trilogy was doing a better job.