Only useful for the bank feature, Mad Moxxi could have offered so much more to enhance the Borderlands universe.
Secret Armory of General Knoxx - 10
The Zombie Island of Dr. Ned - 8
Claptrap's New Robot Revolution - 6
Mad Moxxi's Underdome Riot - 4
Mad Moxxi is definitely the only part of the Borderlands universe that leaves a bad taste in my mouth. I like being able to store weapons at the bank but everything else is under developed and not worth the 800 points.
All you do folks, is run around an open air environment killing spawning enemies. Round after round after round, without any experience or weapons proficiency progress. The enemies are damn hard too, they match the level of the players. It was fun to do the survival modes in the real game as a break, but there was only 3-5 levels in each of them. To get 1 skill point, you have to play through 75 waves of enemies, without any real way to get tactical about it.
The rewards just aren't there, finish a round and some weapons drop out of the sky, but I don't think I saw a single upgrade to my current stash in the bunch. Moxxi can say a few funny things as the game goes on but most of it is incredibly annoying.
If the expansion offered experience, weapons proficiency progress, rarer loot, and more tactical environments (like a cave level), then I might consider it worth purchasing. I recommend saving the 800 points for something else.