I think this idea has some potential, but could use some improvement. The fact that you can reroll at any time feels like a problem to me, since if you get something you don't want, you can just roll again. I think it'd be better if you were forced to use what you rolled before you can roll for another weapon. As it is, the random weapon feels more like an inconvenience but with that change along with some more enemy variety it could lead to some interesting decision making.