One of my favorite things to do is slowly fill the pokedex, this virtually has made me not wanna go back to sun. I'm still trying to fill the Dex in platinum, heart gold, white, white 2, Y, and omegaruby. (Though I usually pick one master copy to fill for each series. For example out of versions with a trio, I always pick the 3rd version to fill. And with how they've been doing it since gen 5, I pick one of the two games to totally complete, and use the other one to play through the story again and catch legendaries.
I've also found that all the games post 4th gen and remakes, are lacking a vs seeker/phone to rebattle trainers.