I recently gave a lecture on shmup development with Unity as part of a course at RMIT University.
You can download the lecture slides and example project.
The example project is a template for Unity shmup development – it contains just a player, an enemy and a scrolling background, however it implements many of the optimizations needed to get a shmup to run properly, such as:
- Bullet pooling
- Collision optimization
- Precise controls
- Transform caching