Thank you for your feedback, I'm glad you find it fun!
As for the aiming system, in the first stages of the game, I thought that it was redundant and unnecessary to have manual aiming when the view port is small. There was some thought about the input, as we wanted to give some level of accesibility by making the game playable with one hand.
About the walls, unless it was an unkown bug, structures cannot be bought during waves.