I have two suggestions as of right now. It's your game so it's up to you in the end, but here goes:
1) Make it so that full screen is unselected to start. I don't know about anybody else, but I use a dual monitor setup, and when it opens in full screen, A) the music is generally blasting and I can't reach the volume and B) all the windows I had opened previously are horribly displaced.
2) Completely eliminate darkness from this game. I understand you are going for difficulty, but imo this is just WAAAY too annoying when you combine it with the enemies firing through walls and all that. You could also leave the darkness in, but make it so that you can at least kind of make out the enemies outside of the circle. Or maybe even a flashlight item that completely eliminates darkness in a straight line whichever direction you are facing? Because I really can't tell you how many times I've had phantom axes/bullets come flying at me, or walked right into one of those chainsaw maniacs who just dashes at me from across the screen because I had no chance to see him coming. I have full confidence that you can make this game just as difficult without the need for obscuring over 50% of the screen.
EDIT: Also, I play the regular size screen mode, which makes things MUCH more of a pain to see than normal. Large screen it fares a little better, but still pretty frustrating to make a jump in darkness just to see a hole appear underneath you while you're running from
an eyeball-demon (don't know what they're called) larger than your entire view.
