You can play every Kingdom Hearts game by owning a PS3 and 3DS. A PS3 gets you KH 1, Re Chain of Memories, and (coming soon) KH 2, and probably birth by sleep included with it.
3ds lets you play Re Coded (just a remake of Re Chain of Memories right?), 358/2, and DDD.
So there you have it. I kind of wish that the hd remixes were available on 360 as well, but that is not the end of the world. I'll probably wait for some sort of mega compilation of every game that will come out some day ... maybe?
3DS is super cheap now, and PS3 is only getting cheaper. These will let you play all of the games in the series (after KH 2.5 releases).
Of course, you will need a next gen system to play KH 3 so that makes it three total systems you will need to buy to enjoy the entire series.
