Heat-Seeking does not work with lasers. Logical but unsure if intended. Heat seeking could also take effect a little quicker, they usually disappear before hitting an enemy.
Turrets can be thrown inside enemies.
Mini-Gun and Heavy-Bullets don't seem to work together, but I guess that would be a little too powerful.
A piercing upgrade would be nice, like a rail-gun to shoot through multiple enemies.
The attack of the bug boss is a bit too fast, maybe a ~+0.15 second delay?
Most upgrades don't seem to do much. Spin-Shot or Circle could maybe have +1 to +2 projectiles per upgrade?
Possibly after dashing you are invincible for ~0.20 seconds, for those times when you dash and barely graze and enemy. This is a better alternative than making the dash longer.
Checkpoints, to add a little bit of mercy on all of our souls. It feels like not saving in Resident Evil and dying and having to restart at the beginning of the chapter.
A magnet upgrade that will increase the range you can pick up Bits?
An upgrade which could slightly increase the tempo, making notes have shorter delays between them.
An upgrade which bullets will follow the cursor for the bullets lifetime.