could use more fluid animation for attacks and arrow flights. Also when rotating the character to attack in different directions they should turn more smoothly/fluidly. Maybe bring the overhead camera in a little closer so everything doesn't appear so small and indistinct.
unbalanced, 40 or 50 dart towers with only upgraded damage let you win without getting hit. Need to limit the max towers you can build and/or have different balloon types that require certain turrets or combo's of turrets to effectively destroy. Has potential with some gameplay tuning.