Red/Green i don't count, they were overall first.
Gold/Silver - Okay, that was cool but more like repairing most Gen I quirks than inventing new stuff.
Ruby/Sapphire - Well, better graphics and... cutting down backwards compatibility? Few side-minigames like Contest?
Diamond/Pearl - P/S Split, some (very limited) use of 3D graphics, menu working with dual screens and again, few side-minigames.
XY - Full 3D, but overall there was no other spectacular changes in gameplay - It was the same old, good Pokemon game, just in 3D, barebone (but imho enjoyable) plot including. Oh, and Mega Evolution but it's just forme changes that we have from gen III, just in different flavour.
...I mean, no? First Pokemon games of every console actualy did not changed anything drastically gameplay-wise, except 3D in gen VI and questionable at best engine upgrade of Gen 3. Sure, the whole series evolved in time, but it was step-by-step process, without big things. There's also the fact that most ideas of people does not work with the core of entire series, and in case of oh-so-glorified open world would outright suck.