The zoom out is too far out, seeing enemies that way is impossible given the colour they are (they blend in), and everything is so tiny when you zoom out. Crystals are few and far between so you can only build one resource per round. I'm not really even sure what the builds do, they didn't really help with enemies. If you run out of crystals (and you will) there is nothing you can do to stop the enemies. I tried blocking them to slow them down but that's doesn't work. Crystals are hard to see as well as they are tiny and again, blend in. Contrasting colours would help with this.

I think the strangest part is the health system. Why it's a giant 3D object at the side of the map only seen when zooming out (the only thing you can really see when zooming out) I don't know. It's a very weird system and having the health at the top corner at all times would be better.

The voice acting is super loud compared to the gentle wind noises. This game would've benefited greatly from some music as well.

I feel like all your points are valid, it was a little bit over ambitious idea at least for me, so I don't have too much time left to game test. the enemy color was ironically last hour change they use to be bright red and I didn't notice that they are hard to see in my last testing.

Buildings are basically towers so you build them close to paths.

Felling strange, cuz you dont know what every tower do. I thing it should be it tutorial too. Also fully agree with "Contrasting colours".
But healthbar looks really cool. Is so unique to show hp like this. And ye, it should be sound settings