Sometimes people will say the non numbered titles in the series are spin-offs. This annoys me and it's an inaccurate description. A spin-off concerns a different narrative, even if there may be some of the same characters. Angel as a spin-off from Buffy the Vampire Slayer, Doctor Who getting spin-offs in K9 and Company, Sarah Jane Adventures, Torchwood and Class. This so far has not happened with Kingdom Hearts, the closest is Union X.
All the console games so far deal with the Xehanort or Dark Seeker Saga, and tie into it even if it's a cutscene at the very end like re:coded. They all add something to the lore that the Dark Seeker Saga uses. Obviously the numbered titles are important, and Birth by Sleep and Dream Drop Distance add just as much to the lore and ongoing storyline, and use new worlds and world designs. Chain of Memories is a bit trickier. While it does recycle worlds from KH1 and exists largely to fill in blanks Nomura realised would be there for KH2's backstory, it still adds a lot to the lore. Introducing Nobodies, the Organisation, Namine, DiZ, kicking off Riku's redemption arc proper as well as first hinting at Roxas and Twilight Town. 358/2 Days and re:coded are more blatant efforts at filling in gaps in the backstory, shown especially in the world recycling from previous games. Days does foreshadow the importance of replicas, as well as the development of Nobodies being able to grow new hearts.
Basically, just because it's not a numbered title doesn't mean it's not important to the overall narrative an if you dismiss a Kingdom Hearts game that's not 1, 2 or 3 chances are you'll be very confused if you only play 1, 2 and/or 3.
Sometimes people will say the non numbered titles in the series are spin-offs. This annoys me and it's an inaccurate description. A spin-off concerns a different narrative, even if there may be some of the same characters. Angel as a spin-off from Buffy the Vampire Slayer, Doctor Who getting spin-offs in K9 and Company, Sarah Jane Adventures, Torchwood and Class. This so far has not happened with Kingdom Hearts, the closest is Union X.
All the console games so far deal with the Xehanort or Dark Seeker Saga, and tie into it even if it's a cutscene at the very end like re:coded. They all add something to the lore that the Dark Seeker Saga uses. Obviously the numbered titles are important, and Birth by Sleep and Dream Drop Distance add just as much to the lore and ongoing storyline, and use new worlds and world designs. Chain of Memories is a bit trickier. While it does recycle worlds from KH1 and exists largely to fill in blanks Nomura realised would be there for KH2's backstory, it still adds a lot to the lore. Introducing Nobodies, the Organisation, Namine, DiZ, kicking off Riku's redemption arc proper as well as first hinting at Roxas and Twilight Town. 358/2 Days and re:coded are more blatant efforts at filling in gaps in the backstory, shown especially in the world recycling from previous games. Days does foreshadow the importance of replicas, as well as the development of Nobodies being able to grow new hearts.
Basically, just because it's not a numbered title doesn't mean it's not important to the overall narrative an if you dismiss a Kingdom Hearts game that's not 1, 2 or 3 chances are you'll be very confused if you only play 1, 2 and/or 3.