So I just beat BBSFM all the way through for the first time. The normal secret ending is the shit, the final story boss fight was redonkulously hard at first, and the secret aqua story doesnt add much.
I think its interesting though that the final mix secret ending is just a trailer for a game that never got made. Its incredibly obvious the way that it flashed between 3 characters (aqua, mickey, riku) all of whom have very clear stories to tell; Aqua travelling through worlds sent the to land of darkness and being a badass survivalist for 12 years, mickey during the events of KH1 and obtaining the darkness keyblade, and riku's travels from CoM to the end of 358/2. Ultimately though, none of those stories really need to be told given what info we've recieved in the other games. I cant imagine rikus story would give us anything we didnt pick up in CoM or KH2, and aqua is limited to doing nothing significant because shes trapped in darkness alone.
Starting up a critical run of DDD now, first I've played it since I beat it at release. Wish me luck, considering how bad I am remembering the right pets to raise.