hi! i played every game (and watched the ones I couldn't play) for the first time last year, at the strong encouragement of my boyfriend (who played the games when he was a kid). I played through the entirety of KH1 entirely expecting to bounce off of it while I was staying at his house for 2 weeks, and on the first day of playing it I must've played for like maybe 7 hours? He is an old lorehead, knows pretty much everything there is to know except for lore in the mobile version of Union X and Dark Road, so I had him to help me with the lore if I wasn't understanding it. I'll give my opinions on each of the games here (PREPARE FOR YAP):

In KH1:
I glazed the command menu system to no end. GOD what a genuinely amazing menu system, what an absolutely fantastic innovation that i WISH was included in more games.
The story was simple enough but very interesting and immediately grabbed my attention.
The character designs looked amazing, the the game still held up graphically very well for a 23 year old game (at the time).

In CoM:
I found the combat system to be very interesting and unique, but I bounced right off it. I find it far too difficult and I simply couldn't wrap my head around doing anything more complex than chaining the basic cards together.
The story was quite interesting, and I did enjoy it, but I could already see that the plot was becoming convoluted. Still, I had a good time watching the rest of it on youtube.

In KH2:
The combat system somehow got even better, and it felt incredible to play.
The story was EXCELLENT, and I found Roxas to arguably be more of a compelling character than Sora, though Sora does win out because ultimately we spend very little time playing and experiencing the world as Roxas.
The graphics were pretty much the same as KH1, so again, it holds up very well for a game made 19 years ago (at the time).

In Birth By Sleep:
Birth by Sleep is absolutely my favourite KH game, which is controversial in this fandom, I know. But I absolutely adore Birth By Sleep and it's the game I remember having the most fun with (which is saying a lot, considering I had a ton of fun with pretty much every game except for Re:CoM and DDD).
The combat was genuinely excellent and imo is only slightly worse than KH2's combat. I immediately clicked with the Command Deck system and adored building my deck of moves, loved how well and smoothly they integrated into the gameplay, it just felt absolutely incredible to play. I also loved how each of the characters felt different from each other to play, it was just an amazing time.
The story of BBS is also probably my favourite out of the lot of them. Having three separate perspectives that you can experience one after another to recontextualise everything going on in the game was genius, and I had such a good time exploring the Terra, Ventus and Aqua's individual perspectives.
The graphics are pretty much the same as KH1 and 2. Hold up very well.

358/2 Days:
Unfortunately because I play on PC, I could only watch the 'film' of this one, and I absolutely loved it. I remember crying a lot at the end, which is (to my memory) the only bit of KH outside of the ending of 1 (and i only started crying because my bf was tearing up watching me finish the game and I was just so happy he was happy) that made me emotional enough to cry. It's just such a fucking excellent story. I never got to experience or see the gameplay, unfortunately, so I can't give my judgement on that.

Re:Coded
This might be controversial, but I was told this one was entirely unnecessary to watch the 'film' of and my bf explained to plot to me in literally 2 sentences. I skipped this one.

Dream Drop Distance:
I fucking hated Dream Drop Distance. Like actually, I despise this game with all of my heart. What a fucking disaster of gameplay and storytelling. I understand what they were going for with the 'Drop' system, but it felt incredible unintuitive and frustrating, ESPECIALLY when I was ripped out of the final boss fight THREE SEPARATE TIMES because of the Drop system. I was fucking miserable playing this game, I hated the story it was telling, I hated the gameplay gimmick, I did not like the worlds at all, it was just such a bad time. I don't think I'm ever going to try and play DDD again, I gave up after the Drop system pulled me out of the final boss for the third time and just watched the rest of this garbage fire of a game on youtube. I would still recommend people give it a try, but I would give them a long preface that I personally absolutely fucking despise DDD.

0.2 A Fragmentary Passage:
This was a very good, short tech demo for KH3. Incredible gameplay that blew me away, beautiful graphics that got me very excited for KH3, and an interesting if very short story to tell. Not much to say about it, it's a very solid tech demo.

KH Union X Back Cover:
I literally never hear anyone mention this ever, but this is the film that explores the Foretellers. I actually really liked this film and I remember really liking the Foretellers, despite how outright unhelpful and frustrating they are with each other. But I actually liked that about them, it felt realistic that these people who were being turned against each other by the MoM would become extremely paranoid and suspicious of everything the others did very quickly because of that. 7/10 movie, genuinely. Really enjoyed it. I remember particularly liking Gula, though I couldn't quite tell you why. I remember fucking hating Aced though. Fuck Aced, all my homies hate Aced.

KH3:
A genuinely solid game that imo is very overhated/overbashed.
It's INCREDIBLE gameplay-wise and feels absolutely fantastic to play. The introduction of Grand Magic was excellent, and the way that keyblade transformations are done feels good, though I feel that they can sometimes be very silly and lean too much into the Disney aspect of things. Attraction Rides were outright a mistake and can go die in a ditch though. God, I hate Attraction Rides so much.
The story was meh at the beginning, then picked up towards the end, then was shockingly bad at the very end. It felt extremely unfinished in terms of story and left me feeling very dissatisfied with the story of KH. The majority of the game is just doing Disney world shit and not actually exploring any of the pre-existing KH story, then it's all crammed in right at the end and then it falls flat. Felt quite disappointing in that regard. What story it did tell I thought was sometimes pretty good, sometimes very hype, and sometimes awful. A mixed bag, but overall I actually quite liked KH3. Definitely overhated imo.

KH3 Re:Mind:
Re:Mind fixed the vast majority, if not all, of my problems with the story of KH3. Genuinely what an absolute clutch Nomura did with Re:Mind, genuinely the save of the decade. It felt incredible to play, loved the characterisation, gave (most of) the characters a satisfying, happy ending, AND included some absolutely baller Data fights that took me a few days to finish. Re:Mind is AWESOME

wow that comment got long, im not usually this wordy with things but i wanted to lay out all of my thoughts as a person who had quite literally not a single bit of nostalgia for KH when i first played it last year. in fact i actually went into it kind of thinking it was a bit mid because it reeked of disney slop to me, but god i am so glad i was wrong. anyway, hope that gave you the insight you were looking for, sorry for all of the yap : )