Batman: Arkham Knight's PC port is really something. WB Games unprecedentedly pulled the game from Steam back in June, when it was revealed to be a very buggy version of the game. Rocksteady have since been working on the port getting it to a place where they are happy.
It is now October, and while patches have been added to the game that help stability, you still can't buy the game on the platform. It seems the end is in sight though. On a Steam Community post, the developer updated the community saying:
While there were significant performance improvements made to the game, the teams are continuing to work on the additional updates that were outlined in our previous post. We expect these updates to be ready at the end of October, at which time the PC version will be made available for purchase. In addition, support for all DLC that has been released for the console versions will be in place.
This whole thing has been a mess, there is no doubt about that. It is good to see this finally being sorted out, but you do feel like the train may have been missed by a significant margin. We will have to see if anything is added to the experience to make up for it.