Hey, great idea for a puzzle game you have thought of here. I could see this being used to make lots of interesting puzzles.
For improvements, other than increasing the volume of the very quiet music by default, I'd say that it would be helpful if the player could open a map to see which pipes were currently active and the positions of obstacles. I found it quite hard to remember the positions of offscreen pipes and barriers, although I am a puzzle noob ;)
Neat game!