Pretty fun game.
I liked the music you chose as well as how you managed to make a relatively cohesive visual style from all the different assets you used. Good job!
At first it was hard to kill the zombies with the magic attacks because I was clicking individually to shoot and the magic balls stopped mid-air without reaching the end of the field. I later learned that you can hold down the attack button and just move.
If that's the intended way of shooting, maybe it would help to just make it autoshoot and the player only has to focus on moving up or down and placing barriers.
Another idea would be have a magic power bar that fills up when you're not shooting and the first shot after a full bar is super powerful and clears a whole row of enemies.
Fun game!