Thanks so much for your kind words and helpful critique - it is much appreciated!
To start, we have just added a brightness slider :) Hope that helps!
Will be looking into solutions for performance issues and your other points! Will add a toggle for the grain too! Bit of a noobie game dev so optimisation is still a foreign language to me to be honest :P
The valve puzzle actually has a note by the window, it was just too dark to see *hides head in shame* Again, major shoutout to you for sticking with it and taking the time to give us your feedback. Thank you!