I like XY and ORAS, but they both disappoint me. I like the mechanics and quality of life improvements, but when I look at story and content as a whole package, Gen VI is a letdown. BW and BW2 beat XY for me and HGSS is a much superior remake when compared to ORAS.
I can't fault XY too much for being light on postgame since the first entries often are, but it's light even as far as light goes. ORAS I can't forgive in terms of postgame or new features, especially after HGSS. HGSS had a whole new safari system, a battle frontier, pokeathlon, pokewalker, a few legendaries and I know there are things I'm missing.
ORAS has soaring and the associated islands... dexnav which is neat, lots of legendaries, copy/pasted Maison(despite being the ORIGIN OF THE FRONTIER), revamped secret bases, a daycare with an infinite loop and uh... ... Oh also a watered down safari zone so that it has none of the safari aspects anymore. Awesome. Oh there's also Delta Episode which was neat.
There's not really any generation I hate. And I don't even know if I'd consider Gen VI my least favorite. But I definitely consider it a letdown in comparison to the things that came just before. I prefer playing Gen VI games due to quality of life and whatnot, though.