I'll tell you what it has lost, the witty humor & dialogue. Both Original Series & Advanced Generation were perfect at humor. We had Savage Ash (roasting his Companions), Incredibly (actually) funny gags and even some mature moments Beauty & Beach, Safari Episode, then there is even that Kangaskhan Episode in which the Kangaskhan Kid jokes about nursing on Misty's Breast in the Original Japanese Version and when the kid meets his human parents again and gets confused, his dad just casually hits him with a branch on the head, hoping to bring back his memories and another funny moment is when Jenny pulls out a GUN and aims it point blank in Ash's face. Can you even imagine current Pokemon doing these sort of things? All of this was lost when DP began, as the anime decided to go on to a more Shonen-esque writing since the Anime was already getting too old by then and many people had already left to watch other things. This is clearly visible in DP, as the series takes on a much more plot-driven, less funny but violent direction, ex: Paul's treatment of Pokemon, Hunter J, Team Galactic and just in general if you look at the first few episode of DP, Ash also has a more aggressive & feisty personality, ex: the entire episode he had an argument with Dawn which was resolved by Nando. Many people think the Anime only tried new things from BW onwards but no, they started trying from DP itself. Then of course we had Best Wishes, where they decided to follow the games and refresh the things for the Anime. After that we had XY & SM, both were which wildly different. When XY started, I think the Staff (realized to an extent) that the Series' Glory Days were over and just tried their best doing the best they could.