Thanks a lot for checking out Twin Ship Shooter, and especially for leaving such a detailed response :)
We're glad you liked it. A high-score or point system would actually be an interesting idea. For the movement: As the levels progresses the level design gets more and more tricky and makes you consider how to effectively position your ships next to each other. This gets especially important for the final boss.
Anyways, thanks for taking the time to leave such a detailed comment. I'll give your game a go and comment on your submission page when I'm done.