The game is really pretty and I like the wave/upgrading system that gives you time to choose.
Regarding the visuals, I'd just like the big asteroids to have a better indication of which fragments are now actually harmful and which aren't. At first I thought the smaller ones were just particle effects but then learned the fragments can still damage Earth.
It was fun to destroy asteroids but it got too hard very fast, with asteroids coming up seemingly out of nowhere. I would feel rather safe by looking at the sonar protecting one side of the planet, only to discover there was already a swarm at the other side. Also, it's hard to control the ship's aim. For some reason it doesn't feel like fires where your mouse is pointing at. Could it be some sort of point tracing bogus with the cam? Especially moving, it gets really hard to hit precisely.
I really liked being able to upgrade the planet, but it seemed not very useful, especially against large asteroids. Also, the upgrading UI could use something like the ship upgrade, where it confirms after you choose. I clicked on some options for a city and had to keep looking at my credits to check if I really bought. It wasn't clear what they would do nor if I had managed to buy.
Regarding ship upgrades, I got a bit disheartened when I discovered upgrading the firing rate removed my upgrade of multiple shots. It could block the player from choosing one if he already got the other.
I couldn't make it past the first 4 waves, are there really invaders or is it always the asteroids? I didn't feel like it fit the theme if it was just some asteroids roaming towards the planet.
One real minor thing, when you lose, the game shows the "wave completed" UI, that felt very strange. I clicked on next wave but at least the buttons didn't seem to do anything. Also, regarding the game over, you could make the point count faster if the player clicks a button, it's boring to be forced to wait before trying again.
Overall it's a nice asteroids shmup. I really like the idea of weaponizing the planet!