You clearly never played Borderlands dlc. It included a new campaign, new weapons, and 3 or 4 new areas to explore. They also included new enemies and unique bosses. You say a character cost ten bucks but playing the game as Krieg or Gaige gave you a completely different experience than playing as Axton, Maya, Sal, or Zero. This isn't to say there DLC was infallible, as Hammerlock's was kind of a stinker, but it added more content than the Dark Below looks to be adding in an expansion.