Quite nice, I must say. Tower defense games like Kingdom Rush is very beloved by me. I gave this game a try, and I liked it. Though, there were some bugs and I have critique:
BUGS:
1) On the same spot can be spawned more than one turrets. It's quite weird 'cause you can not really understand how defended your "path" is
2) My 10-wave challenge has just broken at some moment. Idk what wave it was, but in between the waves the timer has just stopped on 4 seconds. Screenshot provided below.
CRITIQUE:
1) The music definitely does not fit the game
2) Graphics should be better. I suppose you wanted to make it minimalistic, but it's just TOO minimalistic - to the point that you hardly differ turrets.
3) Scale the game a bit down. The icons, text etc. are just too big for the eye - and move everything a bit further from the corners of the screen.
4) Consider adding a label that shows what wave it currently is.
5) Add the possibility to close the tutorial, I had to Alt+F4 and restart the game to come back into main menu!
6) I could not understand what the 4th type of turrets (sniper rifles?) are and how they are spawned
7) Don't feel bad for this project! Consider the critique and just next time use your knowledge!