Kingdom Hearts is a well written piece of art. The idea that Kingdom Hearts is riddled with plot holes and retcons is perpetuated by a casual audience and a cynical fast-paced culture. An audience that doesn't have the time or patience to play though all of the games and fully process the connections being made.
This level of understanding, created though half-listening and misremembering, is parroted to groups that want to tear it down for entertainment. People who've decided, without seeing for themselves, that the story is dumb and overly convoluted. That a "children's game" with 20 years of continuous narrative is bad because they can't understand it with a loose, poorly told summary.
The narrative surrounding Kingdom Hearts is poisoning the narrative contained within it. There is a bias of bad faith shared by millions of people. The story being told is that Kingdom Hearts is a bad story. That Tetusya Nomura is a bad storyteller. This effects how people respond to his style of writing.
Nomura will give the player a question, and the question won't be answered for a long time. (15 years sometimes) The player will then assume there ISN'T an answer. That if the story conflicts with what they know, that the AUTHOR is wrong and NOT the narrator. They don't ask how. They don't ask why. They just say "WRONG".
Kingdom Hearts isn't perfect, but in my experience, every twist is foreshadowed. Every plot point is precendented by prior events, parallels, and well placed symbolism. There is a purpose for what is said and what is done. There is an overarching plan for the story, and it's been around since day one. The answers will come, but they take time.
There is reason not to engage. This story is as old as I am, and unfortunately there have been and will continue to be people who die before they see it end. But there isn't much longer to go. The Lost Master Arc has its pieces in place and they'll be all put together soon. I predict the story will end with Kingdom Hearts V before 2035. Five Acts. Like a Shakespeare play.
But, before that, and I'm calling it now, we'll get Missing-Link, KH4, Re:Union χ [Cross], a cutscene compilation of Dark Road, Verum Rex, maybe a movie?, another side game, and a book.
The series is a time commitment. There is a TON to remember. But it IS made with care, and if you decide to play it and pay attention to it, the story can be very rewarding.