Hi, it's a nice Space Invaders clone!
Even if this makes the game less authentic, I would shape it more dynamically. In my opinion, the fun is very limited otherwise. For example, you could allow continuous enemy movement, more than one player shot at the same time, different weapons, upgrades, power-ups, whatever.
In short, I'd personally add some features that separate the game from the thousands of other Space Invaders clones. The background is already the first step...
