This is from my review of the whole game....
Finally the biggest piece of DLC for this game is The Secret Armory of General Knoxx. This add-on brings you to T-Bone Junction that is connected to other areas by a string of highways with all that road to drive there is also the addition of cool new vehicles like the massive four-seated Lancer. I though got really tried of riding up in down the highways because this add-on has no means of fast travel to the different areas so I ended up restarting the game to cash in missions at the hub area. The basis of the story is that after you have “beaten” Atlas’ commander Steele and opened up the “Vault,” Atlas now wants to take Pandora back and sends the hilariously ambivalent General Knoxx and his Secret Armory full of weaponry to do so. You meet up with an ex-Atlas assassin, Athena, who wants to help you fight back against the Atlas Corporation and General Knoxx. This download adds a lot of new enemy types mainly the elemental oriented Atlas troops to thwart off the repetition of combat. The type of weird humor from the original game is back in this addition with new characters to encounter like Mad Moxxi and the prison keeper, Mr. Shank, who continue to make the world fuller and funnier. I would say this is the most worth while of the add-ons for the game in which it easily adds ten more hours of game play for your Borderlands enjoyment.