The BioShock First Look/Exclusive First Impressions on GameSpot has the promised announcement of the new project from Irrational Games, and though it is not the System Shock 3 announcement that had been anticipated, the game is described by Irrational's Ken Levine as the "spiritual successor" to System Shock 2. They offer first impressions of the game, said to be in development for three years now, as well as a video Q&A about the game with Ken that can streamed for free. Here's a bit from the preview:

BioShock takes place in a mysterious genetic laboratory. Other than that the complex is strewn with corpses (also for reasons unknown), nothing is clear to you. From what you can tell, the laboratory complex is apparently a holdover from World War II--you'll see remnants of the war as well as peeling paint throughout the complex. Something apparently happened back then that caused the complex to be abandoned by whoever was using it. In fact, the complex has only recently come back into use by the scientists circa the early 21st century, and advanced, top-secret contraptions used for arcane biotechnology experiments have been hastily bolted into the rotting walls of the complex.

You'll explore the complex from a first-person perspective, similar to System Shock 2 or Deus Ex, and you'll find it inhabited by three primary "castes" of creatures, which Irrational is currently referring to as "drones," "predators," and "soldiers"--creatures that might once have been human. We were shown a few concept images of creatures that were part human, part monster. Exactly how these creatures came to be this way isn't clear, but Irrational has suggested that some of them are actually fused with human anatomy: human lungs are grafted onto their bodies to breathe, and the human arm dangling off to the side can still hold and fire a gun.