3/5. Fun initially but more upgrades or branched upgrades would be cool. The last 3 stages I had to refresh after every fight because my game would freeze or the frame rate would make in unplayable.
Compared to the initial grinding I had to do to upgrade my dual pistols, that boss was ridiculously easy. It took maybe 15 seconds with a maxed Light String Minigun. Kinda disappointing. 3/5