Short answer: It's pretty good.
Long Answer: It is a interesting concept with fairly playable gameplay and a story so convoluted that after multiple hours of research, I am not entirely sure who is good, bad, and what anybody's intentions are. Now, there are plenty of wonderful games that have a similar situation. Are the ghosts really that bad in Pac-Man? Why must these brothers smash each other? But, a game with a very involved RPG style plot should hopefully be a little coherent. I have played a couple of KH games, read wiki articles, and watched three youtube videos with minimum 45 minute length about the story. I am lost. There are to many X names, nobodies make no sense and i'm not even sure what the situation is going into the much awaited KH3. However I still like the game series overall. The battles are a little chaotic at times. The way to improve your character changes some between games and doesn't always make the most sense, but I have fun when I play them and I like the weird JRPG+Disney idea. It may be my favorite way to consume Disney schtick.
My real problem with KH stems from how much I will put up with before I decide I don't like a game. I like the concept of Kingdom Hearts, I like the battles for the most part, and I like the idea of a weird overarching plot connecting Disney movies and Japanese video games. But, the lack of a coherent plot, awful side features, and really shitty movement I find myself questioning when I draw the line on a game or games. If KH games were something else, I may put it down and consider it crap forever, but I can' bring myself to hate on the KH series. I probably am this way with so many other games too. It's created a bit of an existential crisis for me. What if all the games I like have major flaws but they caught my interest enough to ignore the problems. Perhaps most games are like that and it just comes down to preference.
I choose to end the thought here before all games are ruined for me, by me. None of this matters. The end.