Thanks for your comments! We created a total of 17 levels for this game, so I hope you'll come back to it to see some more of what we have to offer. What confused you about level 4? We tried to convey mechanics to the player through the level design without explicitly telling them, so I hope there wasn't anything too unclear.
Audio was definitely an oversight on our part. We put a lot of effort into making the gameplay solid and the levels interesting, and just didn't have time to think about the audio experience. Something to keep in mind for future projects for sure.