Audio is a bit fuzzy.
The alien ships I liked. So graphics good. I espically liked the background.
Game play..ehhh...its an overused style. Not to say its bad. But in order to make it work you have to add in bits to make it interesting. No powerups. No upgrades.
It stays the same all the way through. Dispite the new enemys.
It does get kind of hard. But with out it staying interesting, no matter how easy or challenging, its going to end up boring.
In conclusion, Its got potential. Add some features, improve on the audio and you have your self a pretty good game. Don't drop this, improve on it first before going on to something else. Good job.