The important XY characters in a nutshell:
The Kalos region, basically tourist France.
Ash, still striving to become a Pokemon master. He has matured somewhat though.
Serena, the new Pokegirl and wannabe girlfriend of Ash. Like May and Dawn, she has chosen to become a contest performer, hoping to become Kalos queen.
Professor Sycamore, the first Pokemon Prof. since Oak twenty years ago to actually do something in the story. He's french, handsome and classy. Currently researching the secret of Mega Evolution.
Diantha, the Kalos Champion. Close friend of the Prof, and is a sugartooth. Knows some stuff about the bonds of Mega Evolution.
Alain, an elite trainer who travels with his sole Pokemon, Mega Charizary Y (Aka Black Charizard) and seeks to beat all the other Mega Evolutions. Recruited into the service of Lysandre upon the premise that he would be able to better mankind whilst becoming the strongest.
Steven, Hoenn Champion and the heir to Devon Corporation. Expert on Mega Evolution stones. Friend of Alain and ally of Lysandre.
Lysandre, the villainous team leader. However, he appears to be an anti-villain who seeks to purge the world of evil. Has convinced Alain and Steven to join him. He apparently needs the power of Mega Evolution to accomplish his goal, though how is currently unknown.
Ultimate Weapon is far too brutal for the anime; hell even Team Plasma's arc was almost completely nerfed into the ground when it came to their dark side of child abuse and Poke-cannibalism. Ghestis was reduced to a stereotypical mind-controlling villain, not the infamous ass we meet in the games.
Lysandre has never actually revealed any dark plans in the anime; the only crime being his grunts having just assaulted Ash for possession of the Zygarde core, the exact purpose of which and how it related to his plans is unknown.