What was your favorite dlc in Fallout 3 and New Vegas? Give reasons, share, explain. Was it the tone, the environment, the enemies, the story, etc.
Mine is Dead Money.
The feeling of constantly being watched... Of being hunted... The lack of trust between you and your fellow "companions"... The excellent story of all the characters involved... And the Ghosts... What's not to love about it?
(I have another discussion idea coming up that will be BIG, some might say like a MOUNTAIN. But that, is a story for another day. Anyways, take a look at those Geiger counters kiddies, and be safe.)
Individually?
Broken Steel in FO3, for it's continuing of the story and feeling finally really taking it to the Enclave. Also, Tesla Cannons. The fall of Liberty Prime is epic, and feeling so involved with the Brotherhood of Steel. It was the kind of feeling I'd end up getting used to in repeated playthroughs of New Vegas in warring over the Dam. The Pitt is a close second, because Purfurator.
In New Vegas...it's a tougher call. Each DLC has things I love and things that drive me up the wall. I'll say that Dead Money has the least such frustrations, and does each of the things you mentioned very well. Plus it lets me buy everything I wanted ever. But I think I have to give it to Lonesome Road. It introduces some of my favorite weapons, armor and characters. I always rolled with ED-E as my nonhuman companion, so that DLC was a big payoff. The setting and backstory are really interesting, if somewhat convoluted. Though it paints a picture of the courier's backstory that not all characters will feel suits them, it usually works fine with my characters, and gives them some "canon" depth without forcing this deep emotional relationship/commitment like the FO3's use of Dad.
I didn't hate it as much as I thought I would. My understanding of it when I bought FO3 was that it was very horror/zombie esque and I really don't like horror/zombie games, so I resisted getting it for a very long time. My friend who got me into Fallout eventually convinced me to try it, and it wasn't as creepy as I was expecting, and the story was plenty interesting. But like the thieve's guild, I played it mostly to get the achievements and haven't gone back to it since. There was nothing in terms of items, perks or weapons that are tempting enough to return for.
That's something I miss out on simply by having no familiarity with that area. Like I've driven through just about all the territory in New Vegas, but I can't for the life of me learn the DC wasteland.
The only shotgun I really use in FO3 is the combat shotgun, and I've never done a melee character in that game; just not a fan of most of those weapons, with the notable exception of the Shishkebab.
Fallout 3 - Point Lookout
A whole new area with interesting side quests, fun weapons (I loved Microwave Emitter), Punga Fruit! :)
Fallout New Vegas - Dead Money
Being forced to survive in Sierra Madre was an amazing experience. Characters were great, weapons were fun, survival aspect was top notch