What I like from DLC is when it offers something new. When it just adds more of the same, it's fine, but it tends not to make my appreciation for the game go up. But there are a few notables.
Enslaved: Odyssey to the West brought us Pigsy's Perfect 10, which took a side character and flushed them out. It brought the character right up to the point where he met the characters from the main game, explained why he was an ass when you first meet him, uses different mechanics that don't get out of place, and gives a lot of insight to a character that only had time for so much depth during the main game.
Mass Effect 3: Citadel--if you like Mass Effect as a series and haven't played this, then you are literally missing out. You want emotional catharsis? It's here. You want the best villain in the series next to Saren? It's here. You want shenanigans, quips, quotes, and most of your surviving crew to show up and pal around with? It's here.
Fallout New Vegas: Old World Blues and Dead Money--these two especially weren't just more of FNV, although that is hardly a problem. These were each themed and poignant in a way that neither Lonesome Road nor Honest Hearts could match. OWB sent you on a quest that made you use all of your skills, and for the first time, it really felt like you could get a ton of use out of putting points into your INT beyond getting more skill points to spend. Dead Money, while dragging it's ass far too damn long for the first section and being full of "do it again, stupid" style traps and an asinine number of instances of being captured in a cutscene, the "let go" theme still resonates with me frequently. Also, there's a way to get a small mountain of gold bars AND to kill Father Elijah, so that makes up for some of the earlier awfulness.
Left Behind--I actually fucking hate The Last of Us. It's a great movie sandwiched between a godsawful, repetitive, horrible game. But Left Behind was amazing, the epitome of what the character moments in TLOU wanted to portray so hard, and it works. It's a beautiful little run with a lot of levity and seriousness in appropriate measure, and it left me dwelling on all the things Ellie has had to deal with. REALLY could have done without more waves of mooks to murder though. I can forgive that in something like Bioshock Infinite, where there's a huge variety of fun ways to plow through waves of mooks, but in a game like TLOU where it's a tiresome chore to actually play, it's just a nail in the coffin. Great DLC, horrible game.
Saint's Row IV: How the Saints Saved Christmas--This...was just fun. Having the boss of the Saints run around in a horrible Christmas sweater was probably my favorite thing to witness this past holiday season. Gold star. Yeah, it's just another excuse to run around in SRIV and I said I usually demand more than that, but...It's the Boss in an ugly Christmas Sweater! That really needs more love.