Honestly, works great! Artwork is sweet and fit the game idea well. Controls are perfect, rescue ship works great for me. Also, the ships avoid collisions very well, good job!
The only issue i had: There was a collision on the far left corner of my screen which i could not prevent, they crashed before i could see them. If you can do something about that, it could be helpful. (although not a big deal, happend once)
If you have the time, you could consider adding some fog maybe? Fog could increase in intensity as the time progresses.