It's a decent start, but there are a lot of adjustments that would make it way better.

• add a way for the player to see what he needs to do to unlock the next towers (this could be as simple as "get to x score to unlock" when hovering over the tower or just right next to it)
• add the ability to cancel the placing of a building, say by pressing right click (it's frustrating selecting the wrong building and then not being able to deselect it)
• maybe add hp bars to enemies (this is up to preference)
• make the end screen go away faster ( I played around 15 rounds and the long end screen made me not want to play anymore)

6/10 for me, I like the direction it is going into, the art style is clean, but it still needs time in the oven, keep it up and good luck on your future projects! :)