Green Man Gaming's refund policy (opens in new tab) states that it does not offer refunds "due to your dissatisfaction with the product or if your computer does not meet the minimum Product requirements." For Batman: Arkham Knight, however, it's willing to make an exception, but not until Warner has had a chance to clean up its mess.
That mess, of course, is the "disastrous" state of the PC version at launch, which we dug into in some depth here. Essentially, the game is playable with some work, but doesn't run nearly as well as it should—and good luck if you have an AMD card. Both AMD and Nvidia have released updated video drivers that better support the game, but the whole thing has the whiff of problems that may never entirely go away.
"Warner Bros. are currently working on a patch which we are hoping will be released soon," GMG wrote in a recent blog post. "We want you to enjoy your game, but if after the fix has been released, you still cannot play your game, we will process refund requests for the game."
The post doesn't nail down the specifics of "cannot play," whether it requires complete non-functionality or just a certain level of poor performance, nor how it will determine the state of each player's game. We've reached out for more information but for now, the safe bet is that if you ask for a refund, you'll probably get it.
GMG also reposted a message from the Steam forums in which Warner offered advice for getting Arkham Knight to run on minimum and recommended hardware. The short version is that borderline systems should run the game at low resolution (1280x720), set textures, shadows, and detail to "low," and turn off all effects; PCs meeting the recommended specs should be able to go to 1920x1080 with normal textures, shadows, and detail, but still need to have all other effects turned off. Warner also suggests avoiding Nvidia's GeForce Experience and AMD's Gaming Evolved tools, and not messing with your page file or any .INI files, "as this will potentially negatively impact performance, including frame rate, and stability."