Very impressed with the artwork. Consistent and pretty.
Not so impressed with the design and the execution. Your game isn't difficult. Your input system is inconsistent. Sometimes, when you press jump, it doesn't happen. Did you put your input inside the FixedUpdate() loop? Because that would explain why sometimes jumps aren't coming out. Further, when you miss a jump, and inevitably fall, you can fall as far down as the beginning of the level. It's not difficult to get back up. It's boring. The second time this happened, I stopped playing.
The music sounds like a collection of randomly placed notes. It produces a dissonant melody that's difficult to stomach over time.
It's a good effort for two young people, but you have a long ways to go.
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I am very greatful for detailed and specific critique of my game. Especialy thanks for the advice with the Fixed update, it bothered me for a longer time. I will take all given flaws and try to reduce them as much as I can in the next game. There just was not enough time to finish and polish the game with my current skillset because I had to learn total basics while I was developing the game.