I really like the gameplay concept, it adds a constraint that really makes the whole thing more stressy. The audio suits perfectly the game. Very good idea !
Though I would have liked some kind of goal other than just survive as long as possible (maybe reaching some planet ? Though it should be hard since the movements are random).
Also I think adding more variety in enemies would be a very usefull. Not just on the number of different sprites, but on their capacities. They are all just moving in a straight line. Maybe some jumping patterns ? Weapons with a definite cycle ? Or size variations ?
I think adding more content to it and a small goal would clearly make me want to play it a bit more than just giving it some tries.