Ok, for a solo dev I think you did a good job. There are things that you need to adjust.
- The physics is too fast and some of it are unreactable like falling for instance, the game does not give me time to react when I fall to my death.
- Camera is too close to the player causing a blind view of the spikes in the level.
- You need to establish the goal for the game. I was confused when I'm looping back to the first level, then I realized the goal is to gathering the highest score from the coins. Also add a leaderboard scores if the goal is that.
- You also need some sound fx for jumping and shooting.
- This is optional but you need a death animation for the player to proses what happened.
That is all, good luck!