The multiplayer element currently requires GOG Galaxy to be running to allow you to even select multiplayer.. I'm a Linux user, and there's no GOG Galaxy build for Linux. This means if you are a Linux user, and want multiplayer, this is a no-go. I haven't got around to playing much of the single player yet and this is my preferred play method (I'm not trying to review bomb) . But I felt the need to leave a review here to inform others. I also hope Shiro Games consider removing this restriction if at all possible, as it doesn't really meld with the "No DRM" ethos of GOG, either.
