Okay, I have more but here are most (lol)
The lack of different female characters: I notice that if you were to line up every exclusive female character in the series (standing at a whopping 7), only Olette and Larxene (and sorta Aqua) have any difference from the rest. All of the others are simply allusions or connections to Kairi, with no one able to hold their own. I'd like to see more girls in any form: villains, allies, shopkeepers, whatever! Suprising how many female fans there are and yet I don't ever hear this...
Cheesy dialogue: Characters always explain far too much (never letting the enviroment or feeling of the moment explain anything), occasionally are repetitive and always stick the the same shtick. Sora love his homies, Xehanort likes darkness, Kairi misses Sora. No one ever has side dialogue that gives more insight into them, or ever speaks casually. Disney has proven themselves beyond simple talk like this, so I don't know what's taking KH so long to follow suit.
My most loathed thing is when someone says something "funny" and everyone stiffs up and does this awful group-laugh as the scene fades out.
Lacking relationships/interactions: For a series that puts so much weight on friendships, it doesn't seem like many characters have any impacting interactions. We're just told they are friends, get a flashback scene of them group-laughing once in a while, and we're supposed to believe that they'd all die for each other. The most striking to me was TVA; I found nothing deep in their relationship and the only reason I knew they really cared about each other was because their bios told me that they do. Because of this I found it hard to really get involved with the story near the end, and only felt bad because of what each went through as an individual (like poor sweet Ventus getting screwed over by his teacher).
The only friendship I found myself invested in is Isa/Saix and Lea/Axel's because of the tensions they end up developing, and the similarities between their childhood relationship to ones I've had growing up, which is more of a personal bias. Also, Axel's and Roxas's because we actually saw it from the beginning and can see why they are close. The extra help from the secret reports written by Axel also were nice.
We also don't get much backstory on anything, making it difficult to understand why people are the way they are (i.e. how they grew up or where they grew up)
One-sided personalities: Everyone suffers from this! I've never really noticed it but everyone's personality is so flat with the exception of Riku. Some personalities I still like for the archetype they bring to story -- most obvious for me is Xigbar/Braig; not really much to him besides "I'm willing to give myself up for a keyblade and I won't ever tell you why [add snarky comment]", but I love that about him. However when most of the cast is a victim of this it becomes a bit old. No one ever doubts what they do, what they believe; no one ever seems to have fears besides just losing to the other side.
It bothers me the most on Sora because he is always described as having a big heart and being open to people. But I notice he has no sympathy for anything except the general good civilians and sticks to Eraqus's similar bullcrap notion of "LIGHT ONLY". It killed me dead when Sora never even once considers the plight of the nobodies... Yeah, they're after him and okay some of them are nasty dudes but, you'd have to be heartless to not even for a moment feel bad when Saix sadly asked for his heart when he disappeared in KH2. I'd have been heartbroken for him, even though he was a general ass (especially when he made Sora get on his knees and beg, and then was like "NO, LOL."). In the end many of them just wanted to feel validated or alive and were grasping at whatever they could to get it, and yet supposedly kind as Sora is, he does not ever listen or even reflect on it afterwards.
The more I replay the games, the less I like Sora, to be honest.
TL;DR: Need more female characters that aren't pseudo-Kairi, characters need more realistic personal interactions, stop making everyone so static
