maybe something for when you upgrade everything? one thing many games do that I hate is when you get every upgrade, it just stops there. Something I would like is when you fully upgrade everything for the first time, some new upgrades become available?maybe you could unlock upgrades per level, so when you have everything and get to the final boss and just can't beat it, you would have some more REALLY EXPENSIVE (because it's so late in the game) upgrades that are really useful and help you along. That way, even people without a mouse could kill the final boss or finish missions. or maybe after you die enough times, something happens that makes the stage easier? I don't know, something along those lines.
Nice ideas, particularly per level upgrades; perhaps I will do this in a future game. I think that having really expensive upgrades to help with the final boss encourages too much grinding, however.
My favorite would be the music. I love how the game wasn't too difficult and tedious, but instead had a steady pace through all the levels. I love randomly finding out that I can eat jellyfish. 5/5.
-cont.- also? the first attack of the 20th level with both types of bullets (they come from the sides of the screen) is the same as clockwork rabbit (imperishable stage 5 boss last word) but without the bullets splitting.
I know it's based off of touhou, (as you can tell with badges 2 & 4, because they share the names of two touhou games, imperishable night and ten desires,) but -will be continued next comment-
 "Deadly Neighbours"){kind=icon}
 "This is the Only Level 3"){kind=icon}
 "My First Quantum Translocator"){kind=icon}
 "Idle Dancing"){kind=icon}
 "Nyos"){kind=icon}
 "Pingy the Ping Idle RPG"){kind=icon}
 "Enigmata: Stellar War"){kind=icon}
 "Tiny Evolution Adventure"){kind=icon}
 "Scraps"){kind=icon}
 "Bloons Tower Defense 4"){kind=icon}
 "No Time To Explain"){kind=icon}
 "Balloon in a Wasteland"){kind=icon}
 "Bullet Heaven"){kind=icon}
 "Bubble Tanks 2"){kind=icon}
 "Gravitee 2"){kind=icon}
Nice ideas, particularly per level upgrades; perhaps I will do this in a future game. I think that having really expensive upgrades to help with the final boss encourages too much grinding, however.