Very good and really frenetic. In the end I was trying to make beautiful patterns with the bullets instead of hitting the enemies.
I think you have made a good system that can be easily expanded with more bullet effects (I'm just imagining the possibilies, things like applying statuses or even a "repeat last n effects" effect would be cool). I think the selection of upgrades could be improved, for example I don't understand how the "reduce size" upgrade could be useful (and its icon is too similar to the increase size too).
I felt a lack of calm moments. I arrived at some point where enemies were continually spawning and I couldn't pause to think up my loadout. Also I sometimes picked up an upgrade by accident because the left mouse button is used both for shooting and grabbing.