An incredible challenge that will test seasoned players and annoy just about everyone.
This DLC is 3 arena stages where you'll at first face 5 round of 5 waves per round for a total of 25 waves. The waves always go in the order of starter, gun, badass, and boss. You receive no experience for kills regardless of your level, which is indicative that this content was designed for level 50 players (despite the ability to play it sooner).
While your initial experiences in each of the three underdome stages might not be so bad, things get annoying after completing the initial challange. Completing 5 rounds of 5 waves in each of the three stages take about 3 hours, or one hour per stage. The next challange is the pain. On the same three stages, complete 20 rounds of five wives per round in each of the three stages. Completing a single 20 round match will take about 5 hours, and that is if you don't die. If you do die it kicks you back one round, but lets you continue.
The problem are many here. The main problem is that it is impossible to organize a decent group of players for the extended amount of time you'll need to complete the long missions. Another is that the game gives the enemies random power-ups, and should the exact wrong combination come up, you're pretty much dead no matter what. The third is that the content is so repetitive and the rewards so useless, its likely most players will get bored even before completing a single maps 20 rounds.
So, while this is a true challange to dedicated players who really enjoy the game, even those players will start to feel the grind before finishing it. Because of the little actual content, the $10 price seems inflated. Even though completing this content will greatly extend the playtime of the title, it does little to extend the actual fun of the game and might just leave the buyer frustrated. To those who are willing to brave the challange, download at your own risk. To those with a schedule and lives outside of the game, don't waste your money because you'll never complete this content.