Really cool that you can stack turrets, it's a really cool idea, but it is not really necessary to use it in practice. Maybe if you could allow the player which direction the stacked on tower shoots, while the 'base' is static could make it more interesting. It's still really fun to get the correct solution to the puzzle, even though I would have to try the same solution multiple times. Cool concept that can be expanded on really nicely, the basics are already there!