People are wondering how the Saga campaign is going to act. Well, here it is without giving much away.The post is too long to quote here, so you can read it in its entirety in this thread.
The demo/prologue is 5 missions. It's 50% instruction training and 50% combat related to the main plot. The reason why it's not a full-blown fight campaign (unlike the excellent Prologue ideas made by our friends in the Standoff team) is because while everyone here is assumed to be used to flying in the SO/WCP engine (and thus familiar with the keyboard controls and all of that), many people will not be familiar with the FS2 controls. That's why this prologue's main purpose is to get everyone up to speed.
There's not much we can do in terms of branching due to the set FS2 engine programming. You either are on the main campaign path, or you are down the path of no-return. As for the main path, let's just say you aren't always winning. And for the path of no-return, it's when you try to defend Proxima and Earth (and lose in the process).