To me, it seems like Phantom Pain makes good on Peace Walker's early inklings of an idea about building a base and managing an army. While that game was mostly sorting spreadsheets during a normal-length, traditional sneaking mission, Phantom Pain looks like it'll be a much lengthier affair with much more time devoted to just being Big Boss. Running your base, recruiting soldiers, actually using your intel teams for valuable information about how to approach the extremely open-plan missions. If you're coming in expecting a traditional Metal Gear setup, the linear trip from opening area to final bossfight, you've got the wrong idea.
I'm hoping the game will actually take place over a significant time period (and we've seen hints of that, like DD growing from a puppy to a full-grown wolf). I'd like to see the game not just be one mission Big Boss went on, but rather a period of time in Big Boss' life.