Great skill-based game, fun and rewarding and you should be very proud of it. Only criticism though is it feels a bit silly how the best meta is to avoid killing the last enemies as long as possible, as then you get enough drops to save up and always have bullets on hand. I died because I couldn't get enough shells for the final boss even with that strat - though I think I could beat it next time maybe...
One more suggestion - it would be appreciated if there was a way to pause but where you could still read the stats and abilities of your various bullets, see what you have etc. - maybe not actually be able to interact with anything, but to let you take stock and plan so you can then execute when you unpause