zomgieee: DLC tends to be terrible value for money and doesn't usually add much to a game.
That completely depends on the DLC, they vary in quality and value the same as full games do, or expansion packs do.
There's no more reason to hate DLC in general than there is to hate expansion packs in general. You should hate bad DLC, or DLC that is a poor value, but that is not something all DLC qualifies as.
Examples of good DLC:
Fallout 3 - Point Lookout, The Pitt, Broken Steel
Mass Effect 2 - Lair of the Shadowbroker, Project Overlord
BioShock 2 - Minerva's Den
Dragon Age - Liliana's Song
ARMA 2 - Mission packs
Grand Theft Auto IV - Ballad of Gay Tony, Lost and Damned
And more.