The biggest flaw by a long way in this game is that you should make it so the mouse click to drop doesn't drag the character to the cursor. This was extremely irritating when trying to control the directions with the keyboard and the drop with the mouse (as trying to drop with the keyboard while moving with the same directional keys is terrible controls)
I tried to enjoy this game, but this resulted in countless deaths that were the game's fault due to control, including at least 3 failed drops a run on the way to fight the boss. Any fun and joy I had to begin with was swiftly replaced with annoyance. You should definitely change this, as frankly it is the single biggest flaw in the whole game.
As for other flaws, it was fun, but the upgrade system was far too drawn out, it literally demanded hours to buy things which again isn't fun, make it so everything is cheaper in future games as the price doesn't add difficulty, it only adds redundant farming. Finally the game automatically threw me onto survival after beating the boss and didn't seem to let me change, considering it looks like a medal was placed for speedrunning the boss, this isn't good.
As for the good aspects of the game, everyone else has been obsessing over them so there is no need to repeat them. A fun game, but in the end of the day made too irritating to want to continue due to the homing into cursor drop.