So do DLC really do more harm than good

would you kindly elaborate on your meaning.

90% of it is crap, but sometimes they'll release something like the GTA IV DLCs that's worth it.

Whenever there's DLC that's minor, such as the Assassin's Creed II ones, I can't help but feel like it was purposely left out of the game just so the developer and publisher can make money off it later. Only when DLC brings major content (GTA IV, I'm looking at you) such that it can almost be thought of as an expansion pack is it worth it.

Some good, mostly bad.

There's nothing wrong with releasing paid/free extra content so fans can get more content for the games they love but it rarely ends there. It's abused and content is held back or locked on the disc to be sold at or shortly after release.

The release it now and DLC/patches to make it complete later attitude is worst development we've seen this generation. DLC can work for games if it's reasonably priced and well done.