Fallout 3's first DLC is a mixed bag of story and shooter elements.
The story is simple. You play a simulation of a 200 year old battle so you can unlock the vault of an army base and gain access to some cool loot. The problem is the Fallout engine doesn't do epic battles. When you strip out the role-playing elements you wind up with a battle that feels like you and a couple other guys against maybe a dozen enemies. The grandness is lost, and at the completion of the simulation, you get a mild twist on the story and a small pile of meh loot.
For the Fallout 3 completionist, you can't go wrong. But this is probably the least fulfilling of the five DLC packs for the game.