I shouldn't really say that DLC made the gaming landscape a little bit for the worse, but there are a handful of DLCs that are pretty worth every single penny.
Fallout 3 Broken Steel is a must purchase for any fans of the game, since it arguable fix the most glaring issue with the game (no after-plot play). Anchorage kinda tried to do a conversion mod-esque plan behind it, focusing more on combat, which is another good waste of $10.
GTA4 Lost and the Damned is like a conversion mod from the PC yester-years, allowing players not only a brand new campaign, but one that's a different feel from the main story line.
But like I said, I think DLCs gives a legitimate excuse for developers to release unfinished content for their games, and later charging a premium to "fix" them. Some are just plainly not worth the money, like more map-packs. Man, I remember having to download free map-packs for UT2k4 that gave not only 6+ quality maps, but a couple of new co-op missions and vechiles to boot.
But yeah, I agree with the article that DLC kinda killed the concept of cool unlockables. I mean, the only unlockables left for some games are features that should NOT be an unlockable to begin with, like the SF4 character line up, or song tracks in GH3 or Rockband that you need to play through in SP before being able to play them on MP, or Zombie Mode for CoD:WaW.
Sorry for the QQ, and really, DLC won't make me stop buying games. But dammit, I want to bitch.