For 400 ms points, the DLC isn't bad. The missions added in aren't lengthy, but long enough to where you enjoy them. The one bad thing about the DLC is the fact iD decided to add in an achievement for completing the game on Ultra Nightmare and considering a lot of people had already finished the game on Nightmare, they must go back and play through the entire game again on a harder difficulty. It's kind of a dick move, but you take the good with the bad, yeah?
tl;dr Yeah, buy it.
We are the Sultans of Swing.