I've never played a game that you upgrade to the point that it takes over and plays itself before. Theres an idle game concept hidden in here somewhere.
Levels are reeeaally long, perhaps shorten them a bit and show us a progress bar. Big rockets seem to overpower supposedly stronger weapons. Other than that I quite enjoy this game!
There is a lot to like about this game. The problem is the general pace and the fact that the endgame is soooo tedious. Bin off the grind of the endgame levels and just have a boss rush. Also give me something to spend that money on. Maybe sink it into artifact upgrades?