Hi, nice effort.
Some of the graphical effects are really nice and I enjoyed the chip tune music.
I would like the background to scroll a bit to give more of a sense of movement - at first I thought I would be able to move in any direction and was confused by the lack of rotation and then asteroids came at me from the side which I thought was unfair - I couldn't shoot them! I also echo what others say about the connection to the theme being quite weak.
Keep on learning and thanks for the fun. :-)