It would be cool if the guns were auto mode, it hurts having to click for each bullet. And sometimes the bullets don´t go where they are supposed to, like having a zombi in front, pointing the mouse directly on it and the bullets pass away. Also an inprovement would be pushing the character backwards and giving some frames of invencibility to avoid the weird to see situation of getting instakilled for 3 zombies. Anyways the upgrade system looks cool. Thanks.
But it couldn´t be on the start? I don´t see the logic, players can already have the same rate of fire without getting the auto-fire, giving it on the start prevents getting handhurt. Mabye it can be balanced by reducing the normal rate of fire at the start, and increase it to the actual state in the upgrade. Thanks.