Not great, but not too bad - the optimization needs a lot of work as well as the overall game's runtime.
I usually don't pay attention to the game's runtime, because if the game has a good story, mechanic or gameplay, I am fine with it. Sadly, the game's description says that the runtime varies around 15-20 minutes - it's not. Even with the overall gameplay time, I managed to find another ending, but still it was less than 5 minutes.
I think the game has a potential. It has a unique set-up, dim atmosphere and good low-poly look, but overall it's not enjoyable.
Best of luck with the future games and I hope you can improve with the new titles.