The story is apparently short and unsatisfying, but it's supposedly all about the side quests.
The story is a bit over forty minutes long, much of which was walking from A to B:
You arrive in the marsh, walk to the lodge, get sent by Hammerlock to kill something only to get interrupted by the new bad guy (who is forgettable enough that I have forgotten his name only the day after). You meet claptrap, boat over to the bad guy's lab and stop his experiment, then go to his other lab (a fifteen minute trek down a linear canyon / cliff side road) and kill him. That's pretty much it.
Also, the loot chamber at the end contained only two average purple items and a whole load of junk. The end boss drops a unique plasma thrower, but it's completely useless as it seems to only fire at the origin of the world (this feels like a bug).
Still haven't done the side missions, but there do seem to be about as many as the Torgue campaign. Some of the new enemies are quite refreshing, but since the story is so short, you don't really see them that often.
Overall the new DLC is a bit unsatisfying.