This is a cool little game! I appreciate the artstyle, it makes the game feel like an illustrated book come to life. I think you did a good job with your tutorial, it clearly explains the movement by letting me experience it rather than just read about it - it did not, however, introduce me to the mechanic of enemies spawning in waves, so I initially just went around to hide in a strategic location thinking enemies didn't spawn in until the first wave had ticked down which both resulted in unnecessary downtime for me, and an extremely difficult time when all enemies swarmed me. It's easy to feel a little lost and far away from the action since the map is quite big, could something more be done here to make sure that the player is always engaged?
The steering mechanic of drawing your route is quite cool, it offers a very tactical approach to moving your tank and it forces you to think about your positioning. While I agree with what's already been said about it being nice to quickly re-draw your path and adjust your movement I also feel that this would possibly rob the spline-based movement of some of its charm. See if you can find a sweet-spot in the middle ground!
For me the game is crazy hard. I wish that I could stay alive longer than i'm able to with my current skill, and if this is something you hear from a lot of your players then maybe consider looking into your balancing for the first waves.
Great work!