Icon Style Study

A "style guide" for icon sets. Certain rules apply to some styles.
One can mix and match different styles or simply follow one. The key is to follow the rules and apply it through out the icon set in a tasteful manner.
One can argue, why use different styles, in one icon set? simple, some icons render better in one of the styles, and some others.

The example Icon on top, follows one of these styles. Thoughts?