It was a challenge, but I managed to complete all the levels, and the game is very addictive. Congratulations!

I think you should add something saying that the player can double jump. Most people don't expect to be able to double jump and therefore can't get past the first part. I enjoyed the game's art the most. Although I do agree that oxygen runs out very fast, but the frequent checkpoints means that it's not as frustrating as it otherwise would be.