This project refactors the "Unity Projects: 2D Platformer" from Unity Asset Store to reduce code duplication and engineer it to follow the component entity pattern. This pattern is essentially the same concept that Unity exposes: you have a GameObject (your entity) and can add scripts (Components) to it. We can abstract out common behaviors into a common class: Instead of PlayerHealth and Enemy containing its own health, we have a Vitality component that handles both cases.

One exception is that Unity provides Components with an Update function instead of having a corresponding System that updates its components. You could still write a System using FindObjectsOfType(typeof(Vitality)), but the documentation warns "this function is very slow". Alternatively, you could have Components register/deregister themselves with the System on in Start/OnDestroy. Neither of these methods seem to follow the core intent of Unity's design and have not been implemented.

• Description of Component-Entity-Systems.
• A concrete example of developing a game using Component-Entity pattern (in ClojureScript).
• Long articles about the what and why of Component Entity System (code is ActionScript).

I've also made some minor style changes:

• Use ToolTips instead of comments on public variables.
• These show up in the inspector to make them useful without diving into the code.
• Use CompareTag instead of string comparison.
• I think the function call is as readable as string comparison and it's supposed to be better for performance.
• Four spaces for indent.
• No space after method names.