The way I see it the burn effect should rather lower current HP rather than the max, or maybe both. Seeing an enemy not losing even 1 point of its remaining life while being on fire is kinda...weird.
I also agree that a repair all button would be nice, or then at the very least a hotkey for repair, r perhaps? U for upgrade defense wouldn't be bad either.
Good game, certainly not too easy. Like its been said before though, more upgrades would make it better still. Other weapons in addition to the beams, homing 'rockets' perhaps? Maybe a mini crab or two appearing alongside you to help.
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