Man, this game has been going to places while I wasn't looking, good job. I could say I didn't understand pretty much anything except I have to shoot monsters, but the very roguelike nature of the game is "fuck around and find out", so it is a feature not a flaw.
I've played 4 levels and died until I realized that there were pickups on the levels I've been ignoring, guns I could have taken, and upgrades I could do between levels. The gun is that good that I ignored all other aspects. Though somehow I began to do worse once I figured out I can have more than two guns, go figure I guess.