It seemed like Pokemon was going in that direction, starting with Gen 5. The story in Black & White was considerably darker and edgier, and it explored some really deep and mature concepts. But then with X&Y, it sorta felt like they took a step back. I mean, I guess it was still fairly dark considering that mass genocide was a factor, like Peitharchia said. But even with that...most of the game felt pretty light-hearted.
I feel like 5th gen is the only one that's considerably darker than the rest, while the others are all about even with each other.