Well
It's not terrible for what it is, a cheap space invaders clone, but it's not very good at all either. I recognize that you put a lot of time into it, but that's game development, that's why it can take years to make a "good" game! Anyway, some improvements would be to the graphics, they don't look so hot. Also, the shots the enemies take don't look all too good, and seem to just kind of 'float'. More levels also would not have hurt! If and when you try again, add something new to the mix, we have all seen Space Invaders before. For example, during each level the 'theme' of everything changes, and there's a zelda-esque trick to winning the level, or something (and definitely a change in music each time a new level starts). Anyway, That's all I have to say, welcome to game design!