Just arrived here, this is excellent, great art style, but has some design issues.
First, as everyone mentioned, the game isn't intuitive at all. And forget about that Controls screen. You need to design a whole level (or several) explaining the mechanics of the game. While I like to discover mechanics, some of them aren't intuitive at all. I'm using a gamepad, besides.
One suggestion could be showing the (A) button when you're on top of Junk, so the player knows he can scavenge it.
You can also throw some text hints on the HUD (per example, when you've got enough Junk, you can show a text "Now you have enough to build your first turret, that will kill those bastards!")
You can imagine the rest, let the game teach the user, not otherwise.
Another suggestion might be take care with the language. You're doing an art style which is a bit "childish" (just a bit) so when the character says "FOCK OFF" it's a bit dissonant. Either balance the language or the art (I'd say the language is easier =P)
But then again, I can see the scope of this game, and I like where it's going. Good luck, mate!