Hey there!
I played your game and can share some feedback :)
Constructive part
* People don't like having to read much.. so while the tutorial is not too large and it looks visually appealing it'd be better to slowly introduce game mechanics during the game
* It felt rather slow. I played one level and at wave 6 I just didn't have anything to do there. Also the enemies felt more like a filler. They did not change what I had to do much, I just placed the units and went to make some tea. Somehow should be more dynamic
* Showing how much you'd get for selling
Positive feedback
+ An interesting two shield system, it does influence what you do and brings some different moves
+ Interesting mechanics that you can and should move the pieces around
+ Visually appealing, nice style
+ You have definitely put a lot of work for finding (or creating) the assets and aligning one to the other
Nitpicking
* On tutorial the button should rather be called close than back
* Scroll on the tutorial is wild, with touchpad it just scroll right to the bottom on a slightest move
* Highliting unavailable units would be nice (like you did with upgrades)
* Button notice -> tutorial or manual or intro? Notice kinda feels not right. I am not native though
* Showing tower range before buying it helps players to make better choices
* I did not get what the other button on upgraded unit does. Extends range? Increases the damage?