I like the graphics, however the pace is too slow to my taste. Also, it feels like I'm going to die whenever there are more than 2 enemies because it takes a lot of hits to kill one enemy. I'd suggest reducing the health of an enemy and adding more of them :D
Otherwise, it would do good to spend more time on details such as hit feedback on enemies and sound effects as that can add a lot to a game.
Thanks for the entry, I'm glad there are 2D shooters :)