It will also raise the level cap to 69 and re-balance the game around this new ceiling. "More than 20 new missions" with "tons of fresh enemies to blast through, including original boss battles, waves of homicidal Claptraps, well-armed Hyperion soldiers, and local creatures that have been Claptrap-ified - including crab-traps, rakk-traps and skag-trapps" will be included.
Those that haven't purchased Borderlands might consider waiting for the Game of the Year Edition, which will be released on October 12 and include Claptrap's New Robot Revolution along with the previous three DLC packs.