You just get from the start that they'll get together, so it is not a surprise.
So why only 4 stars?
Because in this book nothing new actually happens. It is almost just retelling of what has happened in the previous books told from another, Sonya's and Ethan's, point of view.
I said almost because there are a few scenes that are new and that was what made this book worthy of the foruth star. Otherwise it would have been a 3 stars only because I loved the main characters too much and for the writing... not for the hapenings...