This game is really cool , Also loved how you made it look like an arcade game on an old Tv.
Also the pixel sprites were well done, loved the character designs but the tanks... umm not that much.
The music was epic and it kinda kept the mood going.
Also the 1st level kinda felt unnecessary, maybe that's only me feeling that way :(
And the gun looks cool with the sparks that come out of it when you fire, BUT the type of gun is a pistol that shoots bullets one at a time but it looks like an automatic rifle that keeps shooting even though there's not bullets fired of it! Making it look like a automatic rifle but shoots like a pistol unless you pick the "Gun shoots faster" power up , does the animation fit the current profile.
I hope you can make this minor adjustment to make it look much more appealing(Details is key buddy).
The character runs faster which makes up for the amount of damage you deal(Far less damage)
Hence the balance is required here and you made it work!
Anyway well done on your game and good Luck further !