IDK if this is an unpopular opinion here or not but - I do not care for the New Vegas DLCs, do not care for them.
They insist upon themselves.
In all seriousness, I think first of all they detract from the main game. You have this tight storyline about the approaching Battle of Hoover Dam, tensions are rising, the moment of the battle is drawing ever closer - So let's break the tone and pacing to fuck around on a caravan to Utah for no reason whatsoever. Two of the 4 DLCs have you be kidnapped - because that's the only sensical way they could get the player involved in the plot, and I think that's a statement about the DLC formula, that you need to come up with bullshit for it to make sense.
Of the DLCs:
-Dead Money is amazing, the devs tried Survival Horror and did a good job. It always makes me really tense - Having it so your usual tools for dealing with situations don't work is good, I like how each of the companions helps you deal with a specific hazard, I like how you have a Barter/Speech check that if you take it's actually worse for you in the long-run because trying to one-up Dean Domino leaves him bitter towards you, all in all great experience.
-Old World Blues sucks and I hate playing it- So in order to get the Stealth Suit you have to go through a Stealth test and then do harder difficulties to get all the upgrades - This creates the impression that you're going to get a variety of different tools and have different challenges associated with them, but no, you have the stealth segment, then you have this corridoor shooter you're going to have to repeat multiple times and that's it - God forbid we have variety to our challenges. The "Side content" to this DLC is also ass - Go fucking go to all these locations with nothing that interesting in them to find all the Sink Personalities, and their upgrades, it's just fetch quests, worse if you just ignore everything, you get an ending slide telling you how you suck because you didn't explore the map. The game gives you a choice between "Have the Sink be lonely and worthless as a base, or go to all these locations shoot enemies and fetch items" and it just all feels tedious, which is a shame because the idea of having a little base you can upgrade your equipment is decent. The writing and humor can be kinda good, but it also drags on way too much - The most obnoxious part is the intro, where they try to have a back and forth conversation between all the Think Tank, something the engine wasn't made for, plus the back and forth about figuring out the Lobotomy didn't rid you of your reasoning goes on for way too long before they actually realise it.
-Honest Hearts is ok, I find the way the Tribal characters are written a little cringe, and I think having the lives and customs of the local people play second fiddle to two angsty mormons arguing with each other was the wrong call - I want to see the internal struggles of communities be the big driving factor in Fallout, not the two people who actually get to make decisions. I think Joshua Graham is an interesting character, especially since he's one of those "Speaks confidently and charismatically so people overlook the fact that his entire line of reasoning is completely self-serving" types like Mr House - I like characters like that. The Survivalist/Father in the Caves plot is interesting to unravel, but that's all the real side content there is. Some of the quests like finding the missing bighorner calf, or destroying the totems were interesting and I like to see a little bit of variety in your objectives so they were a breath of fresh air.
-I don't like Lonesome Road. It's a boring corridor shooter with a bunch of Deathclaws, and Ulysses is annoying - For a guy whose idea is "Nuke both NCR and Legion and start over", he sure delivers it in the most boring, rambly way possible. I guess it expands ED-E's backstory so that's ok, but it's a different body for ED-E, and also you know, we already see a bit about him in the basegame.
So you got one home run, two stinkers, and one kinda mid DLC. For a series of DLC that are so well acclaimed, and some people say is better than the main-game itself, I find I'm in the minority opinion here of thinking, honestly there's only one of them that I actually like going back and playing.