This is a neat idea, but in my opinion you would need to change or add some stuff to make it really work:
- My biggest problem and what made me stop playing was that I had to restart all over again every time my tank got shot. There is no way to anticipate the timing you will need to avoid getting shot at some point, so you need to let the game run and see if you'll make it, but press pause too late and you won't be able to add the clock you need because your tank will already be on that spot. I think a better way to go might have been to not let the player pause and add stuff after pressing space, but also not removing everything they placed when restarting, so they can just tweak their solution.
- Obviously no sounds makes the game looks way more unpolished that it is.
- You could use the space on the right to add more explanations, it took me a while just fiddling around to understand what I was supposed to do. It's OK to discover stuff by trial and error, but the player should at least have a small idea of what they are supposed to do (I have to praise the use of the rails to guide the player though, that was a cool idea to put them on the right track - pun intended).