Marvel_X saidI'm a fan! I took a chance with KH I and II and totally fell in love with it. The characterizations are awesome, and I found it refreshing to have a serious story mixed with the Disney characters. I'm familiar with the storyline, having played the first two, but I lost track of it with 365/2 and Birth by Sleep.
Oh, and there's a guy on here named Sora...he's a total fan. If you want some fanboy information, hit him up! He's looking for more to add to his crew (e.g. a Riku and Kairi). And I don't think those names are taken...
358/2 Days is probably the saddest one but not really major for the main storyline, just explains how Sora can wield two keyblades in KH2 and some other minor stuff in KH2.
Birth By Sleep is like a major platform game on the PSP, you should definitely check that one out to know what's going on now.
IMO Simple & Clean worked for KH1 and Sanctuary worked for KH2 because they basically talk about what's going on in the story, Simple & Clean being a love song kind of while Sanctuary was talking about nothingness and having those backwards tracks in it saying stuff like "he was ansem"