Oh yeah...I forgot. Aside form the Act, the class, the mystic, we also have 10 additional character levels and with it new skills with their corresponding runes for the expansion.
I hope there's more than that though. The free patch (Loot 2.0, Paragon 2.0, Nephalem Trials, Loot runs) looks really great so the expansion needs to bring something more than that unless the expansion is really light and costs 25% of the vanilla like phatosen said, I mean D2:LoD had the runewords which broken as they are, changed D2 forever.
We need to disassociate the prexpac patch from the xpac itself. When you do that, you'll find that the only thing the xpac adds is a 1 class, 1 act, and the mystic...so far.
I hope there's more than that though. The free patch (Loot 2.0, Paragon 2.0, Nephalem Trials, Loot runs) looks really great so the expansion needs to bring something more than that unless the expansion is really light and costs 25% of the vanilla like phatosen said, I mean D2:LoD had the runewords which broken as they are, changed D2 forever.