So, first of all: The background music might be stuck in my head for days :D
The theme fits pretty good (we also thought about skydiving once). Graphics and sounds are nice and retro.
Also, I am pretty impressed that you managed to create 4 distinct levels in that short time. Well done!
Here some feedback to think about :)
- In space level, some UFOs come from left to right on the same height as the player. And since I cannot move up or down (or can I?), I cannot dodge them. Maybe check for UFO height before spawning it
- The "Wind"-Particles are a nice add on for feeling the falling. However, having a static background destroys the illusion. Making it scroll slowly could do the trick!
Apart from that, good work!!