DLC is always a controversial subject in gaming. On one hand, it's a great opportunity to get more out of the games we love. On the other hand, it can be abused to release half-assed attempts at milking the playerbase.
I'm sure that, despite our opinions on DLC, we all have at least one game that we want more of, whether it's more characters, more stages, more quests, or anything else.
These are mine:
Super Smash Bros Ultimate
I would pretty much buy any number of new characters. Screw tourney balance, Smash is the ultimate party game.
Fire Emblem Warriors
Unlike Zelda, which has a limited roster of potential characters, Fire Emblem has hundreds of characters to choose from, and I would buy most of them. It doesn't help that most of the franchise is completely unrepresented in this crossover, and many fan favorites (straight up popularity poll winners) like Ike, Roy, and Hector are nowhere to be seen. Several such characters were explicitly namedropped as being held back to sell a potential sequel, and if that sequel never happens, fans of those characters just got shafted for no good reason.
As a casual player, I do not care about balance. I like playing characters and gearing them out. So, I would always jump at the chance for new character packs. DC has such a large pool of great heroes to choose from.
Xenoblade Chronicles 2
I wouldn't say no to more Blades, costumes, and quests.
Marvel Ultimate Alliance 3
I know this game isn't even out yet (and we don't know the full roster), but regardless of how many superheroes they have, I would always be willing to buy more.