What is the Borderlands 2 Season Pass?

Because I am all about answering your questions

From somewhere on the Gearboxity page.

After the release of the game, four brand new add-on campaigns for Borderlands 2 are coming your way, featuring new areas to explore, new adventures to undertake, new enemies to overcome and more. Priced individually at 800 Microsoft Points for Xbox 360 and $9.99 on PC and PlayStation 3, these four campaign add-ons are scheduled to hit by June 2013 with more details to come in the future as development progresses.

Soon we'll be offering a "Season Pass" bundle that includes all four campaign add-on packs for 2400 Microsoft Points on Xbox 360 and $29.99 on PC and PlayStation Network -- a savings of 25% over buying each campaign add-on individually. The Borderlands 2 Season Pass will be available through Steam, PlayStation Network and Xbox Live and will also be available at GameStop.

THQ did something similar to this for Saints Row the Third. It is worth it if you are planning on getting all the DLC anyway but, in Saints Row's case it changed the way you have to download the content. Not a big deal but I remembered it as a little confusing due to the strange warning attached to the DLC. DO NOT DOWNLOAD through the Xbox dashboard if you have bought the Season's Pass, download in-game. Unfortunately this warning was still displayed if you were downloading it in game. Even when you were downloading it properly it still gave you the DO NOT DOWNLOAD message. I, of course, blamed Microsoft for this.