Fun and well put together game, there are a few things that'd be nice changes/additions. No drops going off screen, a magnet upgrade, an indicator for when you complete a quest during a run (so you know when to stop after wiping out 5k guys) and a better indicator of where the mouse is (during the really busy stages or bosses it's easy to completely lose where the mouse is)
And most importantly imo an auto merge for equipment during a run. You can be dropping so much but you can't really control what you pick up and what tier they are and with inventory so limited you end up with a bunch of garbage post run despite seeing the higher tier chance drops during a run since it throws out anything that goes over your inventory. Having an upgrade that'd auto merge items as you pick them up would make the system feel so much better, especially if trying to really tier up certain gear.
Until reaching that upgrade whatever point you'd put it at it'd be nice to either have an indicator during a run that shows how full inventory is or a way to manage inventory during a run or at least keep higher quality stuff rather than order you picked it up.
Fun little game though, cheers!