I destroyed the core.
I did a few different runs, after trying a full shield one which made the second to last level very hard, during the successful run I bought damage and firing rate upgrades while also avoiding to damage enemies as much as possible to get a lot of money, except for the second to last level where I actually destroyed enemies so I could win it. I destroyed the core very fast with the weapon upgrades, which makes me think my very first run could in fact could have been successful if I tried to destroy the core instead of thinking I probably could not.
I really like the idea of destroying enemies decreasing money in a game whose main special mechanics is a shield one that you need to buy as consumables, that's clever.
I like the music and the levels are full of visual details. The game is fun and dynamic, there are quite some enemies which work differently. A combination of reasons lead to levels which are ultimately quite distinctive from each other.
In the end the game is very well-rounded, good job.