Classic PC RPG System Shock 2, without which there would be no BioShock series, was released in 1999. It never got an official sequel, but that hasn't stopped fans from putting one together.
It's called System Shock Infinite (cute), and while sharing the same location gives you an all-new story, which kicks off right after the end of the System Shock 2.
There are audio logs, crew members and multiple plotlines, along with the return of System Shock 1's cyberspace levels.
You can download it here.