Hm.. It's kind of hard to have opinions about a game I know so little about. A "rough rough rough demo" is like you said something that will be almost completely changed as progress is made. With this said I figured I'd at least type down some thoughts. None of them will contain comments about the visuals as I'm sure you're already on top of most that we could think about.
* Will we be able to switch between different firepower on the fly? I see you went for a nice spreadshot in the demo, but as we all can see it's not optimal against the boss which is a single, strong, enemy - and not a mass of smaller weak ones.
* I very much oppose the notion of having enemies coming at me from behind. Even in shoot 'em ups where you can shoot backwards that's just really awkward (for me). This is especially true for vertical shmups.
Is there going to be a certain scoring system (chaining, rank, switchable fire modes for more points etc) or just plain "shoot stuff and get points"?