First of all, I wouldn't say that there is any KH game is 'bad.
They are all awesome to me, at least.
Coded was a good game, in my opinion. I admit, the story was a little boring, and quick to finish, but there were some things added in the game that were pretty cool. The secret ending was nice, and I'm glad we finally got to play it -- instead of only letting it for Japan's phones.
I'd give a 8/10 for this game. It wasn't the best KH game, but not that bad, either.