I stumbled on to the Mothership Zeta DLC en route to Vault 92 x number of days ago. I didn't really want to get into it right then, so I just reset and went about my merry way. I got tired of looking at the marker on my map though, so I came back to it today. I've got to say, it was fairly substantial for DLC. Keep in mind, my previous DLC experience is limited to Ratchet & Clank: Quest for Booty and the memory sequences from Assassin's Creed 2. Perhaps the difference here is that I didn't pay $10 for the price of admission since it came with the Game of the Year Edition. Either way I came away from it with a new favorite weapon (Alien Disintegrator), cool melee weapon/armor (Samurai Sword/Armor), a crapTon of stuff to sell, and bright shiny UFO to call my own.
Oh, and for some reason no negative karma (not complaining) for killing/looting Toshiro. Which I was going to do anyway after I saw he had the sword. Win-Win :D