sam

sure! I should clarify first of all that when I said "mechanics" I meant that in a worldbuilding and story sense, not gameplay. thankfully, the cards never come back. chain of memories is the first appearance of nobodies and replicas, both of which will carry forward into future games to varying degrees that I won't get into here for spoiler reasons

it also introduces tons of characters who will continue to be important, and I think it's worthwhile to get their stories from the beginning. are you missing out on a ton for axel if you skip CoM? not really, you'll see him in KH2 and days, but future namine appearances will largely fall flat, and you'd entirely miss out on important organization members like vexen, marluxia, and larxene who may or may not matter in the future, plus the first appearance of DiZ

I think a lot of people have made the argument that, since sora loses his memories in the end, it's not a huge loss for the player to be confused about the same things as him, but I do think riku's story in CoM is pretty crucial to his overall character arc and leads directly into where he's at in days/KH2. not to mention he befriends mickey and it's good to see

I guess I should qualify all of these opinions of mine with, this is the best way imo to experience kingdom hearts if you want the complete story. I know some people don't care about that, which is fair enough but I can't understand it myself

if you're interested in getting the CoM story without playing it yourself, I highly recommend this "story mode" let's play from playframe! he shows off the gameplay just enough to get the idea, while liberally editing out as much of it as possible. if you're not interested... that's also fine! this is all just my opinions