From what I can tell, the only reason I should really play the DS ones is because of story, which I didn't really care about at all from what I played.
See -----> Let's just ignore all that fun gameplay though!
It's pretty laughable that people always put this story emphasis on a series that doesn't have a good story.
Re: Coded has some pretty darn good gameplay.
If you don't care about the story, then skip Days and play the rest.
Chain of Memories is love or hate though. Lots of people seem to dislike it because it's not a buttonmashing fest and actually requires strategy and skill, strangely enough.