The game is ok'ish. From the look & feel I can tell the game resembles the classical dps(damage per second) clicker genre. But It feels bare-bones and unbalanced. Some suggestions:
Try making the reward for each take down a percentage of their life. That way the player can keep up with the increasing costs of the upgrades and the increase in life of the enemies.
Make the player able to revisit earlier levels (and add an advance on completion checkbox). That way you add a strategic choice: Do I go for the better rewards with active clicking, or do I stay on earlier levels to achieve the max rps (resource per second), using pasive dps?
Increase the amount of enemies on higher levels. A standard is to increase in 5 or 10 every 5 or 10 levels (usually sync to the bosses).
Add a time out to the boss. The classical is 30 seconds or 1 minute. The reason behind them is to gatekeep progression. They are usually at the end of a level, not on a level of their own. From there, you can make the boss appear every time or just until defeated. As for reaching the timeout, you can send the player back to the beginning of the level, or force a soft reset (adding a level of prestige).
These are more or less what you will find on any similar game of the dps clicker genre. But remember it's your game. Have fun on your journey!