I like bullet hell games, this is a nice take on the genre! I like the fact that the boss life regenerates so I have to stay focused and avoid the shields.
I'd love to see this more spiced up with feedback and effects (screen shake, some sounds etc.) - at first it was not clear for me that the "link" is dealing damage and i was wondering which button was the shooting button :D
Would be great to also have some variety e.g. deal more damage if I'm closer to the center (more risky position) than staying in back (easier to avoid bullets etc).
Nice entry!