ive installed it from steam many times but i keep getting the same issue "An error occurred while updating monster girl island: prologue (missing Executable)"
I really wish i could help with more but i can't think of anything, MAYBE use different program than winrar? like 7Zip. Doubt that will save you with the exe but i don't know :/. I really want you to play this greatness.
I have no issue over if I'm able to paly. their are some gameplays that I can watch and I'm fine with that. I played the old one and the changes makes me want to play it but I can wait to find a way to launch the new one.