I loved the opening cutscene. An 'ETA' for an extinction event is pretty funny. Like the Defender-esque gameplay, in some ways it feels like a graphical update for an arcade classic! A downside is that there's not a lot of tension here. I wasn't really in danger at any point. It was nice of the second level to switch up the visuals, but it'd be nice to have seen an update to the gameplay. One small thing I could imagine making the gameplay a bit more weighty, is to have there be some kind of penalty to movement during beaming up humans. Right now there's not really any risk to beaming up humans. If I'd be slightly slower, for example, or beaming up civilians would cost fuel I'd have to restock at a place where I'm at more risk of being hit by something, that would increase the tension, I think. The animation for letting go humans before they've entered the spaceship was pretty funny: if you can force the player to 'give up' beaming up humans, they'd see that more often. It'd give the game more of a slapstick quality. These are just ideas, though, maybe you tried them out and they didn't work out! Just my two cents.
Given the time given for development, I think it's really impressive that this game has a very distinct visual style! I liked that a lot.