As promised many moons ago, the BioShock 2 "Protector Trials" single player DLC has been released free on PC, though awhile later than expected, even after the first delay.
In any case, it's here now and contains six new maps, new unlockables (concept art and videos), and seven new achievements. The content itself pits you, a Big Daddy, against waves of Splicers in a bid to protect your Little Sister.
Grab the content via the source or by booting up the game now.
Update: along with the DLC comes a patch which fixes mouse sensitivity and V-Sync issues, among others.