Nice game. The doubling on the intro text makes it a bit hard to read. My biggest problem is that it's hard to not overshoot when trying to aim. I know I got hit by a lot of the smaller rocks because I couldn't point the gun at exactly the right angle. Also, since there doesn't seem to be a reason to ever be not shooting, maybe just have it shoot automatically. I like that the graphics are simple but easy to understand.
Yes, my mother also told me the text was hard to read.
It's true, there isn't a reason not to stop shooting except for the fire rate, but since it's a really small delay between shot it isn't a problem.
I used the commodore 64 palette because I thought it made things easy to see.
Thanks for the feedback!