Actual stakes, Ash being a legitimate experienced trainer, Pokemon battles became actual test of skill and might, and things could go south (I remind Pikachu's assassination attempt by Mega Luke). The whole Lysandre scheme who actually made him batter villain than in the game, a rare feat because the anime tends to nerf their villains because of their younger audiences. I know they decided to go the other route whit the next gen, but is just sad seeing how the anime is just piggybacking in the games, while before it was the other way around, the series brought more audiences to the games