This is nothing to LOL about!
It really depends on the game and the price of the DLC. For instance, in the case of...really, most FPS nowadays, I don't think it's worth it since the price of the DLC is usually more than what the DLC actually adds and the amount of effort to create the DLC (this is mainly the case with map packs). Then there's The Sims 3, which has its store filled with overpriced in-game objects. There's also Fire Emblem Awakening, which I love to death. It is a great game, but it's DLC is overpriced. Luckily, it's not intrusive at all, but there's not much in the way of a reward or content for the $2.50 you pay.
It's like I always say, DLC is a wonderful idea, but when the idea is exploited and used the wrong way or on excess, it becomes one of the worst things that could happen to a game. It can be used to prolong enjoyment in a game, or it could be used to gain money without extorting the consumer via obligatory means. For instance, Dynasty Warriors (the later titles) allow you to buy tracks from earlier games and costumes for your characters. It didn't do much to make you feel that you needed them, it was just something you picked up if you were interested, and the price per item was cheap.
Or how about Elder Scrolls Oblivion and the Shivering Isles? That is the most extensive Elder Scrolls addition to date (even moreso than Dragonborn and Dawnguard combined, I'd say); people even considered it to be almost like an entirely new game. That was an expansion, and while I think $30 is still a little too much too pay for it, its price was justified.
You can make good, justified DLC. The problem is that a lot publishers and developers understand that they can charge exorbitant prices for very little and people will buy the content, as has been evidenced by the Call of Duty (they are the most popular, as well as one of the largest offenders), so they often do the same, which gives a bad name to DLC in the eyes of consumers. Hating all DLC isn't the way to go, but I do recommend speaking out against injustices in the industry, it can only make things better.