Fallout 4's first real DLC, Far Harbor, actually managed to capture the same sense of intensity and moral ambiguity that the base game tried to do with its main storyline, but did it way better. My only qualms were:
A.) Those puzzles in the middle of the darn questline ruined the immersion, IMO,
B.) Even with side quests, it was too short, and
C.) Despite how they advertised the new world space as "the largest they've ever made for a DLC" and all that, there was an underwhelmingly small number of locations to explore. The world space was big, that's true, but the actual, marked, explorable locations on the map were really sparse.
Other than those three things, it was great.
Also, the mods are 10/10.