Ken Levine, best-known for System Shock 2 and Bioshock, is not one for social media. Levine was the co-founder of Irrational Games and led the development of that studio's varied output in different creative roles for almost two decades, before the experience of developing Bioshock Infinite led to the studio's total restructuring as a much smaller operation.
Anyway, before Bioshock, there was SWAT 4: an excellent 2005 game, published by Sierra Entertainment, that was something of a revival for a more sim-oriented 90s series of shooters. Believe it or not, and this is going way back into the weeds now, SWAT began as a spinoff of the Police Quest adventure series, itself intended as an "authentic" depiction of law enforcement, hence SWAT 4's emphasis on proper rules of engagement and tactical gunplay.
SWAT 4 was a critical and commercial success and, as Irrational began concepting the game that would eventually become Bioshock, publisher Sierra wanted another SWAT title. Levine has said in the past the studio also "wanted the money really badly."
Irrational had made several very good games by this point—parts of SWAT 4 hint at the studio's future direction—and didn't want to just make another straightforward entry. So it combined the existing SWAT setup with a pre-existing pitch for a horror-focused shooter as SWAT: Special Division, which would later become known as Division 9. Levine has in the past made positive noises about this project, with a definite 'one that got away' undercurrent, but recently shared the only existing footage of the project and was unambiguous: "This, no doubt, is the best game we never got to make."
This, no doubt, is the best game we never got to make. https://t.co/6Hf6tOyCK1November 11, 2023
A post on the archived Irrational Blog includes the original pitch for the game as one where "Special Division is tasked with protecting the nation against the terrors that do not officially exist." Irrational used SWAT 4 to chuck-together the only gameplay demo of Division 9 that exists in around a week, and yes the similarities to some of what Left4Dead would go on to do are striking. The publisher liked the pitch, and things would have progressed from there, except Irrational got bought up by 2K and from thereon-in focused on Bioshock.
The footage that exists shows Division 9 as basically a slower and more tactical take on monster hordes versus spec ops, incorporating a bunch of original mechanics that allowed it to keep one foot in the sim-shooter side of things while going all-out on the monsters. A neat idea is how members of the squad can now become infected: completing the mission lets them receive treatment, but keeping them alive too long risks them turning.
Following Bioshock Infinite, Levine declared an intention to work on smaller projects, and is now creative director at Ghost Story Games, Irrational's successor. That studio is currently working on Judas, which last year got a reveal trailer: which, for all the talk of "narrative Legos" and a new way of doing things, looks… a lot like an heir to the Bioshock series.