Interesting concept!
You could add a hurt animation for the enemies (a color flash would work) to show that the enemy horde is taking damage, also the healthbar does not seem to update as it is always stuck at full. The enemies didn't seem to respawn after a few waves (is that where the game is supposed to end?)
I can see the potential for the game with this mechanic, but I would suggest to make it so the enemies also have their individual healthbar, when that healthbar goes down to zero, attacking that same enemy will not attack the horde, but the enemy can still attack you, that way it would encourage players to attack different enemies rather than just attacking one single enemy to defeat the whole horde.