Will Kingdom Hearts 3D and Kingdom Hearts Coded have key story information
Will Kingdom Hearts 3D and Kingdom Hearts Coded have key story information
Kingdom Hearts coded sets the stage for what Sora is supposed to do next after KH2. It explains what is in Mickey's letter at the end of KH2 and what caused him to write the letter. However, if you've played BBS and seen the secret ending, Blank Points, you should already have an idea of what Sora's going to do next, so Coded may not be all that important.
As for Kingdom Hearts 3D, we know next to nothing about it except that it takes place after KH2 and Coded. Tetsuya Nomura has likened it to Chain of Memories, so 3D may be to KH3 what CoM was to KH2.