From what I've been able to tell, there is a few Points of Interest needed for map completion inside Fort Trinity that you can't get without getting at least that far in the main story. Or you could find a friend who is about to go there to help you.
I liked the story for the most part. There were only some parts I didn't like and I didn't like how they did the deaths of most people. Though, losing your partner from your order is sad to me.