I think you misunderstood what the story was suppose to be about. It isn't supposed to be about Deacon and Sarah's relationship or even the characters we encounter such as Riki and Boozer, it's a story about moving on. Almost every character we meet in the game is holding onto something from the past. For Deacon, it was Sarah, for Boozer it was his arm.

The open world is repetitive but when you have a world that is as "big" as Days Gone, things are going to get repetitive. And I'm not sure how you were playing the game but the Hordes were intimidating as hell to me. One second I'm just driving my bike, trying to get X place, the next thing a horde is chasing after me. Of course once you develop a decent strategy for dealing with them, they become releativly easy but still.

You can also learn quite a bit about the side characters if you take your time getting to destinations.

The only real complaints I have of the game are that the second half became kind of a slog, and the infinte gas tanks, and hell I got this game two days before it offically came out so experienced it in all of it's bugginess.