Actually, with the latest patch that was released a year ago in December, all bugs that crippled this game and had made it unplayable for PC, have been completely ironed out. I can confirm this as I waited until just after the New Year to buy a Steam Key and the Season Pass. The December patch that was released brings the game version to 1.6.2.0. The Season Pass gave me a whopping number of 32 DLC content, which includes all character skins for Batman, Nightwing, Robin, and Catwoman. Plus all Batmobile skins, all DLC Story modes, the complete Season Of Infamy pack, and all the current challenge modes as well. So getting the Season Pass is really worth it, cause it gives you everything, without having to buy any of the DLC individually.
On top of that, the framerate in the game isn't limited to 30 FPS anymore, and you can actually change it in the game menu now ! You have the option to set the framerate all the way up to 90 FPS, which is where I set mine at, and the game runs real smooth. It's really incredible !
The game also has a Photo Mode feature where you can take some pretty amazing pictures while playing the game, this was never in the originally released game. So this is a really cool addition for the re-release and patched up game.
If you are looking for any existing mods for the game, the only ones that are currently available that I know of, can be found on YouTube with download links and instructions on how to use them. These mods will allow you to use any character, even villains to play as in the game. Want to play as someone else other than Batman from the get-go ? No problem, just use one of the character mods and you are good to go !
When on YouTube, just search for something like Batman Arkham Knight Mods, and you will come across a number of good ones that you can use for the game.