Obviously spoilers for the first 3 games, just in case anyone is like me and playing through for the first time. And sorry for the wall of text
(So far) Kingdom Hearts 1 seems to be isolated with CoM being a direct sequel and Riku's portion seems to start at the same time, but continue after Sora's. 358/2 Days seems to be end of KH1 and continues well beyond CoM and Kingdom Hearts 2 is a direct sequel to 358/2 Days..I think.
My understanding of the story so far..
Riku hates being on Destiny Islands and lets The Darkness into him, along with Ansem, who wants to join with Kingdom Hearts, the Darkness that everything is born in and dies in, which kicks off the story. The Disney baddies also want this, I'm assuming we'll later get a solid connection between the 2, because as of now, I don't think they've explained how Maleficent and Ansem were intertwined and seems to be played off as either coincidence or Ansem pulling the strings from behind the curtain.
The plans are a bit confusing to me, KH1 using the Hearts of all the Princess' to gain access to Kingdom Hearts, while 358/2 The Organization are just releasing the Hearts from the Heartless. I guess maybe a Princess of Heart's Heart is just worth a shitload of normal ones?
The Kingdom Hearts itself is also a bit unclear to me, 358/2 says it's basically where all Hearts go after they're freed, it's Light and not Darkness like Ansem believed..So I guess Heartless are to Kingdom Hearts as Moths are to a flame? Which might also be similar to Nobodies who want Kingdom Hearts in the hopes of getting their own Heart, except they just want to devour it?
This brings me on to the Nobodies, losing your Heart makes you Heartless, but I'm still unclear on what creates a Nobody. They put a lot of focus on Sora unlocking his heart to release Kairi's at the end of KH1 (They showed that smile after he stabbed himself like 4-5 times..I get it, guys), so I'm assuming Nobodies are formed from the separation/disconnect of the Heart and not it's complete loss. Roxas' introduction made it clear he was Sora from the beginning, I figured Xenmas was Ansem's Nobody immediately after seeing his name, reinforced later learning Axel's name was Lea. Most of the others in The Organization are still fairly blank, mostly because of how many there were and how infrequently they popped up for short times, usually just the little text bits over screenshots. Their plan other than wanting Sora's power is still a mystery and I'm looking forward to finding out more and hopefully it's more than using the Keyblade to unlock the Door to Darkness again.
CoM's story while a bit mind-bendy, still seemed relatively straight forward. ”Here's what you did in this world, with a slight twist..wait..is that how it ended?" seemed to be the recurring problem, the slight twist either being the order of events, the lack of certain key characters, and each seemed to end somewhat happily, with nothing leading towards the actual ending of KH1. The overall story being that Marluxia wants to use Namine to make Sora into his slave through altering his memories and take over the Organization, to what end, I don't know. Bad guy loses, Sora chooses to regain his lost memory and takes a nap while Namine fixes things.
Riku's CoM story was more personal and internal, revolving around conquering the Darkness within him. Meets up with Mickey, then chooses the path between Light/Dark. In 358/2 he's basically poking and prodding the characters toward the conclusion. I was a little confused with Mickey seeing him as Ansem, having been right after Xion was shown to mirror other people based on their perception, combined with being called an Imposter over and over I thought it might have been another Puppet, but seemed to be the real one in the end.
I liked the relationship between Roxas/Axel/Xion. Roxas being the Nobody of Sora and Xion a puppet to emulate Roxas, leeching off some of his memories/power and morphing into an image of Kairi was interesting, the knowledge that you play as Roxas at the start of KH2 and Sora in KH3 leads me to think what happened with Xion merging with Roxas is going to happen with Roxas/Sleeping Sora and he'll turn to crystal/glass/ice/whatever and disappear too. The story was all over the place, but seemed mostly about Xion developing her own personality while she and Roxas grew together before returning to where they belong. The ending though, I'm not sure and I'm guessing it'll be explained early in KH2, with Roxas suddenly waking up as if he were a different person immediately following 358/2. DiZ also seems to be Ansem, there seems to be 3 worlds, Light, Dark and Twilight. Dark being KH1 Ansem/Riku, Twilight being Xemnas, so I'm assuming for now DiZ is Light Ansem.
So...How far off am I so far? Anything I misinterpreted or missed completely? I know there's likely going to be some retcons and revelations in the games to come that might change events I've seen already.