Love how well the mechanics play into each other, constantly putting the player in a state of calm and vulnerability while in attack state, giving some risk vs reward elements, making the gameplay more dynamic. The boss was pretty fun too, especially the last attack phase where you force the player to have to make use of their absorption ability to eat all the bullets before going for an attack and trying to dodge all remaining bullets to survive while trying to get back your shield.
I thought it would be interesting to have different enemy types/behaviours that would challenge the player's playstyle and powers instead of more of the same enemies except with different colour and shapes firing slightly more bullets.
For example an enemy that would come up to the player and be able to damage you even through your shield, which might force the player to impulsively attack quickly, opening themselves to incoming damage.
Or perhaps an enemy that could fire bullets that can overload your shield if you were hit by it when your energy has already filled 2 bars.
And lastly an enemy that can only be destroyed by your attack if you have released it at 2 bars.