Cool concept but if I wanted high score I won't switch weapons. You could add a level system and have the weapons randomized each level. Also, you could implement a system that forces the player to switch between weapons. It could be something like, when spending 1 bullet with mouse weapon, recharge 1 bullet of keyboard weapon, obviosly depending of which weapon you are using.
As an aside, the "play again" button doesn't work. If you haven't solved it yet, it could be a Time.timeScale is set to 0 or a panel or something that is blocking the button raycast. Or that you forgot to add the OnClick method to the button. Anyways, good work!