You should add some sort of checkpoint system or something that helps you dodge bullets better. The enemies seem to track you through walls and arbitrarily shoot you when you get whatever distance close to them. Your game is pretty difficult in the beginning, maybe make structure the levels so that each level is progressively harder.
The character movement should be more precise to make it easier to strafe and peek walls. I feel like making the bullet go faster would actually make me feel like an actual gunslinger.
The game definitely needs some sort of death sequence or transition to game over. Show your character exploding or whatever and give everything some sort of player feedback. Giving visual feedback or reaction to something makes a game feel nicer to play and gives it s o u l. Don't just instantly show a "you're dead" screen.
Just keep iterating on your game and implementing good player feedback. I think it'll eventually turn out okay.