Deep Silver and Techland have announced that Dead Island's Bloodbath Arena DLC pack will be released in "mid-November". While this is a decent delay from the original planned release in September, they noted that this extra time will be used "to make sure that every Dead Island fan will receive the best experience possible on every platform".
This is obviously referring to the recent launch issues the PC version had, as well as multiple problems on the PS3 version. Of course, the developers are still working on patches and will hopefully be able to achieve a stable experience on all platforms for both the main game and DLC launch.
Bloodbath Arena will be available free to those who purchased the special edition copy of the game and is expected to cost $10 for everyone else. The DLC pack includes a new weapon, separate leaderboards, and 4 arenas where you'll fight waves of zombie attacks:
"...the Bloodbath Arena pack features single and multiplayer challenges in four different arenas. It’s a pure fight for survival when wave after wave of deadly zombie attacks, one more gruesome than the next! Characters can also gain additional experience points and items and bring them over to their single or multiplayer campaigns. What’s more, players can show off their skills in zombie fighting via the Bloodbath Arena’s Leaderboards. Finally, Bloodbath Arena includes a new exclusive weapon, the brain wave bomb, to ensure some highly explosive combat experiences."