I am one of first backers, but I have only played Book 1 and waited till now for playing more. Book 1 worked great on Linux with Intel HD graphics, without any problems and with good performance. But now I am unable to play :-( Without any parameters, game freezes after title (never gets into menu, but music still plays). With -force-opengl parameter it does work, but it is really slow, nearly unplayable (even on lowest visual settings). Looking at other discussions, it seems that problems started with Unity 5.
This problem is widespread, see e.g. discussions here:
Please can you test your game on Linux with Intel HD graphics and fix this problem? How hard could it be for you to acquire some cheap Intel laptop / desktop and debug it? Intel HD graphics has really good support for OpenGL on Linux (with latest stable Mesa 12.0 drivers it fully supports OpenGL Core 4.3, see here for more info: http://mesamatrix.net).
Without your help, I am unable to play the game that I helped fund (promised Linux support has been main reason why I funded it). Please do something with it, those discussions where people reported this problem are from december 2015 and nothing has happened since then!
I can help you with debugging if you want, just please please do something...