It's a cool simple game and fun to play. A few things that are required to make this game more interesting and achieve retention are -
- Make the Movement controls more responsive.
- In the beginning, have some Lil space for the player to move around and reduce up the enemies.
- Ramp up the difficulty slowly, don't do it from the very beginning.
- You can add some visual effects when the player is jumping higher.
- Also, a few interactive sounds can be added to this game to make this feel more awesome.
- You can try different animations of the player jump, which would make it feel more natural.
- Also, why not add some cool powerups to this game?