The game is not bad. Graphics and music are good. The game is challenging. However, you need to explain better what the player has to do (as MarksmanM said). The first thing which shocked me was the Play button. Why not writing "Play" in the circle ? Why do I have to wait 5s to see "Push here to start" ? I clicked two times on the star because the first time I played I didnt wait so I didnt know how i reached the credits (and when i was on the credits, i had to imagine clicking will make me return to the main menu... no "Back" button...)
Keep in mind that players don't know your game, your thoughts. They need instructions. But you made something well : the city level, before the planet menu. It can be used as the tutorial level.
And don't forget they have "standard shortcuts" :
Esc / P - Pause
M - Mute
R - Restart level
Spacebar - Next level
This make your game more intuitive.