recommended for: people who want to play in release order, people who want to start simple, people with normal amounts of gaming time, people who want the gay boys first and foremost

why should i play this one?: the original Kingdom Hearts follows wider series protagonist and lovable goofball boy Sora (no last name given) as he bounces from Disney movie world to Disney movie world fighting darkness with his funny key sword, solving their problems and searching for his friend Kairi and unknown crush/cool rival Riku after the three's home is swallowed in darkness.
it is a pretty simple start to the long-running franchise, only beginning to poke its nose into the bigger lore picture that had yet to entirely congeal into Something. the hacking-and-slashing gameplay is still rough at the edges, but even here it's starting to take shape. it's a pretty soft introduction, so if you just want to start on the meat of the franchise this is where it all begins - if you like this one, you'll love the games to follow.

where can i play it?: if you have any of the listed systems above, great news - it's available on all of those! PS2 emulation is shaping up pretty well AFAIK if you don't feel like/don't have the space for buying or Otherwise Legally Obtaining ;) ;) ;) the HD compilation release(s).

suggestions on where to go once you beat it

• i want to continue release order!: play Chain of Memories for the GBA or the PS2 remake, depending on if you think you'll prefer the 2D or 3D card combat system (people like the 2D original more, generally!). after that, play Kingdom Hearts 2, followed by 358/2 Days, followed by Birth by Sleep... you can figure it out from here. this is probably the best way to watch Sora and Riku become more obviously gay as time goes on tbh, this is really kind of the intentional order
• i'd like to continue the story, but don't want to quite stick to release order! lay the complexity on me: still play CoM - if you wanna avoid the card game for now i'd recommend playing 358/2 Days (not just watching the HD cutscene movie - see the Days section) which bridges the same span of time and provides different context to Kingdom Hearts 2. but you are good to jump straight into KH2 if you like.
  play Birth by Sleep whenever you feel like it because it's Important, dip into re:coded if you want but you don't have to - just make sure you've played KH1, Days, KH2 and BBS before you play Dream Drop Distance, which is what i'd call the series bottleneck where everything prior really *comes together*, and it'll get real confusing from here on without the context.
• holy shit i loved that secret ending concept trailer thingy?? how do i get THERE: you're going to be wanting to play 358/2 Days. the game EXISTS to justify that secret ending and it kind of owns for that. after that, either play CoM for context on the first part of Days, or KH2 if you want to pick up right where Days leaves off. again, do BBS when you get to it, etc etc, just make sure you're all caught up before KH3D.

recommended for: people who want to be put in the character's shoes, suckers for a slow burn tragedy, people who play games in short spurts, fans of black outfits, transgender people

why should i play this one?: KH Days here stars a boy named Roxas, who has literally just started existence as an empty shell, getting sucked into doing fieldwork for a shady Organization consisting of fellow people who do not have "hearts", falling in with older brother-type Axel and fellow no-memories Org newbie Xion who together try their hardest to stay together even as their world falls apart around them. the story overall is about Roxas's quest to figure out anything, Xion's struggle to define her own identity as a person outside of the expectations the authority figures have for her as a mere tool, and Axel's slowly widening distance from everyone - whether it be his new friends or his old ex-boyfriend it's-complicated Saix.
kh days throws you right into the meat of the confusing metaphysics, but importantly it's putting you in the shoes of someone who has just as little of a clue what's going on as any newb, making this game a whole lot more... verisimilitudinous? palatable? if you're playing it as your first. days's gameplay might wear on you in longer sessions, but it's meant to be played in shorter bursts of a few missions at a time, so take it slow, ok?

where can i play it?: nintendo DS only. there's a couple-hour HD cutscene compilation available, but it misses a lot of the smaller interactions and moments that absolutely MAKE Days into what it is - the longer slow burn is what makes it, so if you're making it your first entry you will be wanting that DS version.

suggestions on where to go once you beat it

• who is Sora? what happened to the C.O. team?: play Kingdom Hearts (original) (see entry on that) and Chain of Memories for the GBA and PS2. after that, play Kingdom Hearts 2 to catch up with Roxas and finally see where everything goes. after that, play Birth by Sleep which should clear up a few mysteries, then optionally play re:coded before you reach the series bottleneck that is Dream Drop Distance - it incorporates enough of all the prior games that the context of at least KH1, Days, KH2 and BBS really helps.
• i'll find out who Sora is as i go. what's Roxas getting up to i am ITCHING to know: jump right into Kingdom Hearts 2 for the conclusion to Roxas's story if you're really that dedicated to finding out, then hopefully fall in love with goofy dummy boy Sora to go back and check out KH1 and CoM. then Birth by Sleep, then Dream Drop Distance.
• wait, who's that kid that looks like roxas in that one moment???? is that roxas in a different outfit or?????: play Birth by Sleep for that bit of context. BBS is a prequel to the whole series, and does retroactively tie up a few tantalizing loose ends Days dangles for you (as it does with. afterward, you should probably just continue forward chronologically with KH1, CoM, and KH2 (and maybe re:coded), going right to Dream Drop Distance after.

recommended for: people who want a Lore foundation, star wars likers maybe?, himbo appreciators, chronological order people, people who like to mess with stuff fusion-synthesis systems in games

why should i play this one?: birth by sleep is about Aqua, Terra, and Ventus, the three disciples of one of the few remaining Keyblade masters - once the proud stewards of the world in the age of fairy tales, now relegated to little more than a few members of the old guard in large empty holdouts with only a few disciples (think of them as being a lot like the Jedi, just encouraging connecting with others instead of isolating themselves). old man Xehanort, the 'brother' of their teacher Eraqus, seeks to isolate the trio from each other so he can use each for his ultimate plan - reaching the heart of all worlds, Kingdom Hearts.
as a prequel, BBS requires no knowledge of the stuff that takes place after chronologically to dive into, and it builds up a lot of lore stuff around light, darkness and the silly key swords if that's your dig. its "command deck" gameplay is also the basis for the next few games that come after it, as the first outing by the dev team that would be handling the games from then on. you can play for longer stretches than Days but still - pace yourself, since the tree main chars have interweaving stories to run through that covers a lot of similar ground

where can i play it?: like most of the other kingdom hearts games, BBS is available in HD compilations. the original PSP version is also still quite good, and the emulator PPSSPP runs pretty well on mobile so you're good to bring it on the go.

suggestions on where to go once you beat it

• feeling like chronological order: Kingdom Hearts 1, Chain of Memories, 358/2 Days, Kingdom Hearts 2, re:coded, Dream Drop Distance, Kingdom Hearts 3. this is the easiest the order possibly gets.
• wait, what's the Keyblade War? what's that whole deal?: play watch the cutscene compilation that is Union Cross - what remains of the mobile game. it's VERY lore-important, but also so distant to the past that it's kind of something to tackle on your own time. after that, see chronological order.
• so how does Aqua turn out in the end?: see chronological order, but sneak a playthrough of Kingdom Hearts 0.2: a fragmentary passage in there after KH1. really everything after BBS is some variation of "chronological order", so unless you're feeling adventurous that's about the best advice i can give you for order to play 'em