First of all I have to say, I just loved the fact that you started out as a head!
A shooting head, but just a head nontheless, which is cool!
I thought the idea was a good one too - instead of starting out as a cannon, airship or whatnot shooting something - you're just a head. Easy to upgrade from a head, ain't it? And that would be the point of the whole game - to upgrade yourself from a barely moving head into SO MUCH MORE! Having all this take place in a junkyard, just makes you think how wacky and inventive these upgrades could be.
Wacky they were at times, the pop-culture refrences were funny, and not overdone. On the other hand, you could have gone somewhat more overboard with different upgrades. All the upgrades seemed to consist of building up your robot, but other than adding defense - and the one time ability to move faster, the upgrades seem repetitive and somewhat useless.
Since basically, most defense games of different kinds, usually are based on how enjoyable the upgrades are - this game kinda missed the spot.
But the potential is there!
As I've said, starting out as a head is an excellent idea - makes it funny too.
And a junkyard is a perfect setting!
Try perhaps to go CRAZIER with the upgrades.
Instead of building a regular robot - really build him out of scraps and pieces as the junkyard setting directs.
Have one arm bigger than the other, weird kind of legs, which aren't the same length - made of pipes, crowbars and just plain junk!
And of course, give the upgrades MEANING!
Upgrading feet could possibly upgrade speed instead of only defense, adding arms could possibly add extra weaponry (weaponry which has some kind of actual RANGE) etc.
The player is supposed to really want to upgrade, and frankly - upgrades here felt kinda dull, which is a damn shame since the idea was EXCELLENT!
I liked the music by the way, very fitting.
Basically what I'm is with a wackier set of upgrades and allaround style, adding meaning to every upgrade (more than just defense)..this game would go from a GREAT IDEA with potential to simply a great game.
Hope to see more from you in the future, and keep on making cool games!