DLC is fine when used right. If it adds a significant amount to an already good game and if it's worth the price, I'm down. Fallout is a great state example, you essentially pay, what, £5 and you get a new area (essentially a small open world) to explore with a storyline, new content, enemies etc. Most range between 5-10 hours, which is amazing given the price and can be integrated within the main game.
An other good example is GTA V, they essentially had around 10 small DLC packs, which added new vehicles, clothes, guns, game modes, properties etc. and guess what, they were all free. That's not the end of it either, two major components to online (game mode creator mode and online heists), that weren't finished upon release, were also released down the line for free as well. That's a great gesture from Rockstar, yes they have have microtransactions, but they balance out with tons of free content and regular updates. You feel like you're not losing out.
So two great examples above, but that's not the bulk of DLC. A lot of it is a cash grab, especially when the game is lacking content and then they release that content as purchasable DLC; I hate that. I judge DLC on a case-by-case basis, if I throughly enjoy a certain game, and they release DLC, then I'm going to buy it most likely. If I'm playing a game I'm enjoying, but the DLC seems lackluster and overpriced, then I'm going to back out. Simple.