Nice game,
I think it needs some feedback on enemy hit as at first I thought flamethrower doesn't damage the enemy tanks and only later realized that it does.
The minigun upgrade step doesn't really feel like an upgrade, maybe it is stronger than the flame thrower without having AOE but it's really hard to tell.
And it feels like either the enemy health is too big or the weapon too weak, (maybe flipping the evolution order would be nicer)
The art style is nice though and it fits the theme nicely.
Good job!