The Borderlands 2 DLC, much like the previous game, is a mixed bag. But unlike Borderlands 1, all of them suffer from having gigantic empty areas requiring a long hike to the next place of interest. The pirate DLC is good and has some of the nicest locations such as the crystal caves and challenging boss fights. However, the Sir Hammerlock DLC is junk and looks like something one person whipped up in a week. It's the perfect example to level designers why bigger does not necessarily mean better.
That said, if you enjoyed Borderlands 1 I recommend getting the inevitable GOTY of 2 on sale. It's fun and way more polished.