It would be nice that when there's a Boss, enemies keep on coming to keep earning gold to still be able to upgrade units and/or fill empty spots and/or replace a unit if its killed, and also so the units don't get bored while the Boss is at other line.
If not, that the Boss itself drops coins while it loses health.
It's kinda annoying that some bosses bullets are the same colour than your's, and that some abilities like "line blast" doesn't let you see the enemy's bullets, it should destroy them or at least let you see them.
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I'm glad zomeone notized! :)