Whee! This one was a lot of fun.
I think the core gameplay loop you have here works very well. The two phases of gameplay are pretty different, so that keeps things interesting, and I think the short duration fo each loop keeps things moving too. I did find the chair a little difficult to control after the space launch, since it doesn't follow the mouse directly - maybe having an upgrade path to improve the tracking could be interesting? I think having some more sound effects for destroying objects would be nice too, to improve the variety.
The graphics are basically perfect, I think. Bright colours and low-poly 3D works very well for the genre.
Are you planning to make a mobile version? I think this could work very well on a touchscreen, since the controls are fairly simple, and I could see myself playing this while waiting for the bus.
I'll leave some feedback over on the Google Forms link too.