Fun game, the lag gets frustrating when you have a bunch of spinning coins, unfortunately stacks wouldnt work with some upgrades, particularly collapse. Also, Factory Premium can cause issues, especially with Collapse where it grinds the game to basically freezing.
It would also be really nice to be able to select multiple coins to pay, once you get above like 10 it can be really tedious to pull that many individual coins.
On the whole, a fun idea and neat execution. Some weapons feel worse than the base pistol. A few things I found during play: holding enter after selecting ammo lets you continue to buy without wasting ammo of your equipped weapon. If you exit to menu and come back, bought upgrades revert to original price until you buy one of them and bought weapons show up as unbought, although you can still equip them. Finally, if you have a sword equipped and drag out of the games focus, the weapon doesn't do the attack.
