Not so bad
Of course this is'nt a big game but I think with some improvements the version 2 will be cool.
Here some ideas/advice that I can give you :
#1 : Have an option ON/OFF for the music.
#2 : It can be cool to have saucer stronger than others.
#3 : Having a reloading time.
#5 : Adding some upgrades that we can buy between levels can be interesting.
#6 : Graphics is not so bad, but I think you can do better (saucer's nice, but not the trees lol).
In general, not a bad game but it miss something for making it more interesting.
I hope to see your next version soon :).