There's something weird where if you fall from a platform without jumping, you fall really fast. I would recommend adding a few more assets to the game and keeping it to a single level while you work on trying to adjust the feel of the game. When it's this early in the development stage, your primary focus should be on making the game FEEL good. It should be responsive, intuitive, and satisfying. A few things that could help your game to feel better as far as player controls go are to decrease the amount of time it takes for the player to reach the ground after jumping, but leave some hang time, or adding a slight acceleration and deceleration to the horizontal movement. These things help keep the movement from feeling static. I take it based on you not having any other games on your profile that this is your first attempt at game creation at all. Stick with it! Once you get the feel down it becomes very rewarding to make a game. I hope to see you continue to work on your game development skills!