I came up with the following features for my game (Priority top to bottom):
- Movement
- A goal to finish the game/a level; Basic obstacles and collision handling
- More advanced obstacles (e.g. moving ones); Multiple levels
- Energy which must be filled up with pickups or by completing a level fast
- A menu
- Some background music and basic sound effects
- Animations/Particles
- Boosters/Pickups (e.g. ability to fly through obstacles for a few seconds, slowmoe…)
- Enemys which try to fly into you on some parts of the level
- Parts of the map where you need to “fly around corners” (with the camera following to a different “side” of the level)
