Surprisingly difficult, but I did manage to beat the first campaign boss. More UI around Energy management would have been helpful. Since the main strategy of the game is shooting until you are at around a quarter energy, then dodging / shielding until it fully refills, it would have been great to not have to keep looking in the lower left at a grey bar to manage it. Something more front and center with colors, and maybe even an indicator as to how much longer it will be before it starts to fill.
Also, selecting "Restart" after winning the campaign just shows a blank screen, and the game needed to be closed manually.
(These comments refer to demo version released around 8/15/2021)