Pokémon X and Pokémon Y

I wasn't too fond of Diamond and Pearl either. I think it kinda lost the charm of the earlier games. The region was boring as heck and not memorable in the slightest (literally the only place I remember is the snowy town), the pokemon designs were like 50% just evolutions of past pokemon and had far too similar designs (Magmortar, Abomasnow and the Electrabuzz evolution spring to mind) and another 15% were all legendaries (far too many legendaries, and only a few were cool, like Shaymin and Darkrai)

And while the battles and overworld were probably about the same speed as the 3rd gen, the rather crappy 3D sprites made the games feel way more clunky and slow than they were before, which is what made me prefer the HG/SS remakes over Diamond and Pearl, because they improved on the 3D graphics and made it feel more like the earlier games. They included everything that was introduced in Diamond and Pearl while keeping with the feeling of 2nd Gen. which worked. it worked really well.

I definitely feel like 5th gen was a success too, the decision to start fresh with a new roster of pokemon was a good idea, and we got some really amazingly designed pokemon. The region wasn't particuarly large or exciting, but it was easier to traverse and the game flowed a lot better. Black 2 and White 2 took this even further and were the most enjoyable pokemon experience I've had since I first got Pokemon Red when I was a kid.

In my opinion:

1st Gen > 2nd Gen > 5th Gen > 3rd Gen > 4th Gen