Okay I'm going to walk that back only slightly. The one DLC in Fallout 3 that I actually enjoyed was Operation Anchorage but that was only because it changed Fallout 3 into a straight up FPS game. Point Lookout could have been interesting but it was short, tiny, uninteresting and full of godawful fetch quests.
Mothership Zeta? Oof. just... fuck. badly balanced dlc, awful level layouts. No interesting lore. And the alien weapons look like ass.
Don't EVEN get me started on Broken Steel holy fuck.
okay actually another point for Operation Anchorage in FO3, you got some fuckin' sweet loot out of it. that gauss rifle oh my god I loved that weapon. Also kinda liked that because it was a simulation written by some rabid, racist knobjockey it was a full on pre-war propaganda piece, so full of horrid stereotypes and "FUCK YEAH AMERICA" bullshit, lol and it was internally consistant with Fallout's crapsack world.