Fallout 3

I never understood why so many people hated the Mothership Zeta DLC, putting evil space aliens into a post-apocalyptic setting seemed like a perfect fit.  The world has been destroyed by war and on top of that the aliens decide come at finish the job. 
 
Yes, it's mostly combat focused but the feeling you get from exploring the futuristic space craft is well worth the time and money.  The interior of the ship follows Fallout 3's 1950s style of what may remember seeing in old sci-fi movies of the era.  You'll encounter all sorts of people who have been abducted from different time periods and you will have work with them to get off the ship.  There is a little girl named Sally who will serve as your guide aswell as opening locked doors enabling you to explore more of the ship.  There's also audio logs scattered through out each deck which tell you a little bit about the people who were abducted. 
 
Story wise it's pretty weak however the it's really the sense of mystery that makes it so appealing.  It's really just like a classic sci-fi b-movie where you don't know the aliens' true intentions but they obviously don't like humans.  Only thing that annoys me is how you get negative karma for killing alien workers, it's like the devs just threw em in there just because morality is one of the core parts of the game.  Maybe there was an option to negotiate with the aliens then you have a reason for not shooting the defencesless workers but as far as i can see the whole story is based on "aliens=bad".  Aside from that though i think this DLC was well worth it and anyone looking to get the FULL FALLOUT 3 EXPERIENCE should buy it(or if you don't wanna spend all that money just get the GOTY edition).