I've played and beaten:
KH: 1 PS2
KH: 2 PS2
KH: Chain of memories GBA, and Re: Chain of memories PS2 (Rebirth mode)
I want to get:
KH: 358/2 days DS
KH: Birth by sleep PSP
KH: Re:coded DS
Coming soon:
KH: 3D 3DS
Personally I don't mind fillers and I love this series if you haven't played kingdom hearts please don;t judge because Disney characters are in it it's an amazing Action/RPG.