Here's my rating:
The gameplay was interesting although basic, with no real innovation. The comets come out of nowhere and are very hard to dodge. The tank controls would work if it weren't for the fact that the velocity made no physical sense. If you turned left, the forward momentum also turned left, which meant that you were going forward even though you turned around. It doesn't sound all that bad, but it feels terrible. There's also the fact that I couldn't harvest planets even though I was supposed to be able to, which is a rather major bug because I couldn't earn points. My rating: 3.5 (rounded to 4) stars.
It fits the theme. My rating: 5 stars.
Holy cow, the graphics are amazing! Seriously, great job! The style and usage is consistent, and it feels very well made! I am left wondering a little though, because I know that Kenney assets exist, and this art looks very much like that.... But I'm not here to point fingers. My rating: 5 stars.
The audio was pretty lacking, the biggest factor being the total absence of music. However, the existing sound effects were somewhat decent. My rating: 2.5 (rounded to 3) stars.
Overall, this game looks really good, but the lack of good audio to back it up and the very untuned controls (not to mention the big, fatal bug) really beg for fixing. My rating: 4 stars.