What I think of DLC depends on the developer's philosophy. The 2K method of taking content from the game and reselling it later for no other reason than to make profit is bull crap. This also applies to things like $15 for a map pack.
Now if it's the Gearbox method, then I'm perfectly ok with it. IE, the developer does not put any work towards DLC until the main game is completed and on the market. Then when they do release DLC, it's always in the form of a expansion pack that justifies the price. Case-in-point, all 4 of Borderlands' DLC Expansions add something major to the game, 2 of which adding onto the actual story.
The 1st, Zombie Island of Dr. Ned, added an expansive new area with a variety of enemies to fight. The 2nd, Mad Moxxi's Underdome, added a bank feature and the Underdome; this one mostly served as a multiplayer-based expansion. The 3rd, The Secret Armory of General Knoxx, well...
The trailer says it all. The 4th, Claptrap's New Robot Revolution, finally allowed the fans to kill Claptrap as much as they wanted. They're all relatively cheap, and all add something substantial to the gameplay, story, or both. THAT is what DLC should be, as opposed to overpriced map packs or cosmetic stuff that no one cares about.