This update adds a whole new "story mode" (which is actually just a fancy way of saying "easy difficulty setting") to the game.
It's for all the people who want to experience Beyond a Total Loss for the story/humor/sexy dialogues/stellar graphics/god knows what, but don't want the hassle of actually PLAYING THE GAME. Well, that's not entirely true. You still have suffer the gameplay to some extent and you can still die in all kinds of horrible ways, but staying alive & murdering your enemies will be a lot, a lot, a lot easier.
And that's it and that's all (except for a few superficial improvements).