So a genuinely, constantly hot topic is Downloadable Content. It started years ago with map packs and various other addons such as skins and whatnot, but it's much more than that now. Right now the target is Batman: Arkham City and the Catwoman DLC, but there will be something new in the not to distant future, so here's my two cents on it
A few years ago EA started Project Ten Dollar. Buying a new EA game gave a few nice perks. With Mass Effect 2, there was free access to a lot of DLC and the Cerberus Network (the in-game DLC store). However, there is no way to gain access without either a brand new game or $10. So that's ten bucks on top of however much the rest of the DLC costs (although there was plenty of free DLC as well). The reception was luke-warm. No one really complained, but not everyone was happy with EA. For the most part, the Project Ten Dollar games could be played without any of the DLC and the game was still great. Nothing major was ever taken out of the game
Catwoman (alongside the skins for Batman) is the project ten dollar for Arkham City. Catwoman is a playable character and several objects and areas in game are made for her, as well as some of the open world puzzles like the widely dispersed Riddler Trophies. This is fine, I'm okay with her having that stuff with her DLC. The big issues is that they exist in the game no matter what, even if you don't have the DLC. Batman can't collect these objects or prizes or access these areas correctly. It's very silly for this stuff to be here when Catwoman is not.
Many other companies started to copy this idea, because it is a decent idea. Publishers don't get revenue from used game sales, on the retailer. This way a publisher could get some money off of a used game. But this is around the time where DLC was sort of polar. Either DLC was very good or it was ridiculous.
There is a lot of flaming about DLC on a whole. No matter what the DLC is, it's often argued it 'should have been on the disc.' Sometimes this is true, like co-op modes, extra characters or extra chapters do feel like they were just ripped from the game in order to have DLC to sell after the game launches. There is still DLC that does consist of those things and is great, but still argued whether it should have been DLC or not.
I don't normally buy DLC, I don't like the idea of it. I'm a liar, of course. I've bought loads of DLC for games I love, but that's what happens. You want more content for a game you love? Why not pick up the DLC and get something more out of it for a few hours. I'll admit, there is plenty of DLC out there that is just random, stupid or cosmetic that I have bought, but I don't normally regret it. The DLC is there for the people who will buy it because they love the game. If you didn't like the game, don't buy the DLC.
Map packs are one of the few things I won't excuse though. I don't think maps should cost money. But I'm a PC gamer and most of the best maps are user made and great companies like Valve add great maps regularly free of charge.