OK. Realizing this was an alpha build makes not want to be as bad to this game, as it is clearly unfinished. So, instead of a critique, heres a few pointers, the music is not that bad but the high pitch 8 bit noises noises can get irritating and ear numbing, it sounds too much like just a whole bunch of noise. The ship could have tighter and faster controls, I feel like Im diving a toy car through a swamp, and this game should have a faster pace, maybe not a bullet heaven kind of fast, but still, you should move faster, the enemies shoud respawn faster, and have more variety, seeing as they follow you slightly maybe you should try adding some kind of suicidal one that tracks you around and blows up for a large amount of damage. Last, you shoud rebalance your weapons, the deafault peashooter does its job adequately, if a bit nerfed for my tastes, but when I got the first upgrade, I just held the fire button, while pressing alternately pushing left and right and just sweeped the screen like that.
As far as the background goes yours is good, some of the debris from the asteroids are a bit confusing but still, not bad at all.
Ultimately this game could go on to be a preety good one some day if you dedicate enough effort to it.
Ill give it 2.5 stars now and change it later if I see enough changes have been made to it to warrant a revisit