>>717006428
If I were to make one, I would try:
1. Make the movement of the ship/character respond well to the controls (many shoot 'em ups fail at this most basic point, such as the terrible Sky Force series).
2. Add types of enemies that work together well (older shoot 'em ups used to launch waves of the same enemies at the player, which makes the experience much shallower).
3. Levels should always have action. (in games like Gunbird 1, you can kill enemies quickly once you memorize the levels, and the screen ends up empty in several places)
4. Levels should be well designed and challenging, in addition to the bosses
5. Bosses should be fun
6. There should be a training mode for levels and bosses
7. There should be a game mode that shuffles the pieces for when the player has mastered the game but wants to continue experimenting with it in less "serious" way
8. Sexy women and lots of nudity and bouncing boobs