While Kusaka was trying to recover from that mess that was Black&White by writing BW2 and, at least, close the circle of the story in Unima, he probably had a nervous breakdown and started to reread his whole work, trying to find where he "lost the touch". For me, the manga started to run out of steam since Emerald, not the saga, the character, unlike Yellow he was totally not needed, we already had Wally who was instead thrown out of the window. However, the Emerald story itself worked because it was the cool final battle of the three dexholders trios, ending with 30 volumes, OCD power I call you. Every story written after this was too bound to the game it was based on, it became too simple, too linear and even tying the villain’s plots to the original characters was blatant fanservice. Every arc started to be like a commercial for the game. XY is a great return to the past, the story of Kalos is a story played by Kalos characters in the Kalos region, those few "guest stars" are there not because they're tied to the events by some new revelation on their past, but because they became, through the past events we already experienced, important figures of the Pokemon world, therefore their role is to aid the new characters instead of overshadowing them. Talking about the actual protagonists of this arc, I would not say they are very original, since both X and Y have an aspect of Ruby’s background, but still they’re not cheap characters, their motives are believable and their actions are well weighed. About the villains you cannot do very much giving the original story of the XY games, Ruby&Sapphire suffered the same problem and that arc was much longer than this one. On my point of view, the success of this part derives from its conciseness, it succeeds in giving us two full fledged protagonist and a bunch of good secondary characters in a short but intense story, and the tension is created ALSO because this story is original, it’s not the gym tour of Sinnoh and Unima (and partially Hoenn, Sapphire storyline IS kinda weak on that front). The change of rhythm from the main storyline screams that this is the kind of story Kusaka wants to write and what is his vision of the Pokemon world, the care he put here made me love XY manga so much that it become one of my three favourites arcs in the entire series, despite the fact that the XY games are the worst. I hate France.