Finished :-) You asked for feedback, but I honestly can only think of compliments. Your game looks fantastic, it plays and controls really fluently, the music and sound are great and, most importantly, it did not get repetitive at all. It provided just the right amount of incentive to remain curious and motivated to get further and upgrade further. So, really well done!!!
It did trigger a lot of ideas to add. Like puzzles, enemies, more incentive to kill in a specific way, powerups that are dropped, etc etc ... But, at the same time, the current simplicity also has its charm. If it gets too complicated to manage stuff the game might lose its attractiveness, for me at least.
Very solid basis for more I'd say! Definitely wishlisted :-)