I don't often post here, but this topic definitely sparked my interest. Overall, I really enjoyed XYZ, probably more than I have any Pokemon series in a long time. That said, it definitely had a few glaring problems:
1) The treatment of Noibat/Noivern - Easily the worst development of any of Ash's Pokemon even though he hatched when Ash only had four other Pokemon! I can forgive the fact that he didn't win very many battles, as he was a baby, but why didn't he get more than two episodes of development? And more importantly, why didn't he have any personality? Like, at all? Such a waste of a perfectly cute/cool Pokemon...
2) The treatment of Goomy/Goodra - Unlike Noibat, Goomy did have a personality, but not one that I liked and although he was around for, like, 15 episodes, he still got more screen time and development than Noibat. And leaving him at the swamp (even though I didn't like him) also seemed like such a wasted opportunity.
3) Serena's Eevee - I like Eevee as a species, but Serena's was annoying and got way too much screen time. How many times do we need to see it act shy around new Pokemon? Or run away because there were too many people and it got scared? I mean, its not a BAD personality, it just go old after awhile.
4) Serena yelling at Ash for daring to be upset that he lost a gym battle/couldn't make Ash Greninja work - Rant incoming! This was the worst moment for me, bar none. "The Ash I know is always positive and never gives up!!!" So, being angry/upset and wanting time alone for, like, a few hours makes him suddenly "not Ash anymore?" Um, way to deny his perfectly legit feelings, Serena (especially considering that he's, you know, 10)! But that wasn't the bad part, oh no. The bad part was that her "pep talk" about how its absolutely not okay for him to have any negative feelings what-so-ever actually WORKED! Okay, so yes, maybe I'm projecting a bit, but I hate, hate, HATE when media for children spreads the message that its not okay to have "negative" feelings. Maybe the show didn't mean to imply this, but that was still the nasty implication that came across. I mean, did we learn nothing from Inside Out?