Following a false start, an "interim patch" is now available for the Windows edition of Batman: Arkham Knight, which was so broken upon release, sales of the superhero sequel were suspended until things could be sorted out. As the interim tag suggests, there may still be issues, but this should address a variety of problems. This Steam Community Group Announcement from WBIE has the details:

Good news - testing for the interim patch has been completed and it is now available for those who already have Batman: Arkham Knight for PC. As a reminder, below are some of the major fixes and improvements that will be addressed with this patch:

Reduced frame rate hitches
Optimizations for system memory and VRAM usage
Improved performance on all GPUs (requires the latest drivers)
More Comprehensive In-Game Settings
Fixed low resolution texture bugs
Fixed hitches when running on mechanical hard drives (HDD)

In addition to the above, we’re continuing to work on the following for future updates:
Adding support for SLI and Crossfire
Adding support for the latest DLC & Season Pass content
Adding support for additional updates such as Photo Mode
Continued improvements and bug fixing for a Windows 7 specific memory issue that occurs on configurations with 8GB of system RAM and some NVIDIA GPUs during extended game play
Continued improvements for Windows 10 specific issues on systems with some AMD GPUs

As always, we will monitor for any additional issues that come up and will provide further optimizations and bug fixes along the way.

We would like to thank everyone for their patience and invaluable feedback. We’ll provide ongoing updates here as they are made available. In the meantime, please enjoy the game with the latest patch.