we already know from the back of the box that we are going to "enter the service of Saruman the White", so surely there has got to be a big twist at the end of the cycle, when we discover that Saruman is not all he seems.
I play LOTR online, and they have a similar story on there (it's been a while since i did it), where you end up getting captured and imprisoned inside Isengard, and you have to fight your way out. I reckon it's going to be something like that... at first we will be fighting the enemies mentioned on the back of the box, but then we will somehow discover that they are the good guys and get imprisoned in Isengard. Then the big battle in the 6th pack will actually be inside the tower, fighting against Saruman to get our way out.
Maybe they will have another go at an Escape from Dol Guldur type quest -- where one of our companions starts the quest in a cell.