Very nice, it's fun to play.
Adding sound and bosses could really bring this to the next level as a tower defense game. But in it's current state it's already enjoyable, though after a while it does start to lag a lot. Perhaps changing difficulty by transitioning to stronger enemies and stronger projectiles instead of increasing the amount would help performance.
The minimalistic sprites are readable and work well.
One gameplay remark, the beggar, or old man with coin only comes facing to the right, so that created a bit of an uneven battlefield, which could be interesting, but left my left side rather empty with very few turrets.
Here's a screenshot just before I stopped due to lag: https://imgur.com/a/s2wzONl