Digital Extremes, the team behind Dark Sector, the PS3 port of Bioshock and co-developer of the first 3 Unreal Tournament titles is working on a Bioshock Multiplayer for Bioshock 2.

While details are still sketchy, the multiplayer mode is expected to contribute to the overall story of the franchise by being placed as a prequel to Bioshock, with snippets of story line and information to be gleaned from locations, scenarios and characters. 

More details, yet to be released, are expected to confirm the specifics of the multiplayer modes. Some ideas being banded around on the internet currently involve modes in which one player will play as a Big Daddy with other team members competing again him and each other to take him down, a plasmids Vs weapons mode, bog standard team deathmatch and a VIP style mode in which one team must protect a Little Sister against the other.  I'd definitely like to see the appearance of a “Nazi Zombies” or “Horde” style mode  in which you fight as a small group to stay alive against increasingly difficult waves of enemies. With the different levels and grades of enemies I think this would work well. It does seem to have been confirmed though that there will not be a co-op option within the actual campaign mode. This doesn't bother me too much – using the first one as an example, having a team mate with you would potentially ruin the atmosphere and feeling of the game. 

The action will take place before and during the fall of rapture as you play a Plasmid Test Subject for Sinclair Solutions.  You'll earn experience points for kills and actions in the game which will allow you to access new weapons, plasmids and tonics.  One possible scenario for this is the COD4 and COD5 route which sees an ongoing development taking you through a lot of gameplay hours.
Whatever the details of the multiplayer, my prime interest in Bioshock 2 is the single player which will hopefully deliver another quality outing in Rapture.

On a related note, it seems that the working title “Sea of Dreams” has been shelved and the game looks set to be released simply as “Bioshock 2”.  The game is still expected to arrive sometime during Q4 of 2009 on Xbox 360, PS3 and PC.