'Humble' is not a word I would rush to associate with Borderlands, given the chest-thumping, max-volume mania of 2 and the recent Pre-Sequel, but in this instance it means you can lay hands on the bulk of Gearbox's FPS/RPG series for few-pennies.
Paying what you want - i.e. anything from $1 and upwards - gets you Steam keys for Borderlands 1 and its purportedly much-improved DLC. You'll have to beat the average price - currently around $6 - to get Borderlands 2 however, but that gets you three of its nine DLC packs plus, confusingly, a coupon for $75% off third game Borderlands: The Pre-Sequel (which would bring that game's price down to around $15).
Pay $15 or more and you get the rest of the BL2 DLC and 25% off merchandise from the 2K store. More thingers are due to be announced on the 30th, and the bundle becomes an ex-bundle on Tuesday July 7th.
As always, you can split your financial vote to apportion money wherever you prefer, in this instance between 2K Games, The Videogame History Museum and Humble themselves.
I don't particularly enjoy the Borderlands games because I like a quiet life, but don't let my old man curmudgeonliness bother you, eh?