I personally love this game. It has a fantastic soundtrack, great art, smooth gameplay and is an all around fun game.
My major problems with the game, though, are tied to gameplay. The game is less hard and more punishing. Any game with bullet hell aspects or enemies that all can deal combat damage should have a period of damage immunity and a clear sign of taking damage, neither of which this game really has.
My second major problem with the game pertains to the power up system. While the power ups are well executed, there are some that are near useless, broken, or simply don't work sometimes. Rebound is a power up that is better in its ideals rather in function. Every time I get it it hardly does anything useful except for the spread shot and often is extremely confusing if there is an abundance of enemies on screen. I found myself actively avoiding the power up just on that premiss. Now the shield power up... It's great, well designed and doesn't show up enough to make it broken, but sometimes... It just dOSEN'T WORK. I have died numerous times with the shield and it drives me insane! If this is a purposeful feature that's bad and misleading design. If not? Fix it! I imagine it wouldn't be too hard (not saying any of designing a game is easy) but REALLY.
Not to leave it on a bad note, but that's just about it. I lived this game, would recommend 100% just try and keep those things in mind developer(s).