The SitePoint PHP blog has a tutorial posted introducing some of the updates to the theme functionality in Drupal 8 including some new features.

If you are a Drupal developer who has dabbled in theming older versions of Drupal (5, 6, 7) you understand why frustration is the trusty companion of any Drupal themer. Luckily, though, Drupal 8 promises so many improvements that even the Angry Themer is happy for a change. It is only natural we jump in and start looking at what these improvement are.

They talk about the changes in:

• creating a module and defining its theme
• that Twig is now the template library
• updates to template handling
• how to debug themes/templates
• working with assets and libraries

Each topic includes a summary of the changes or more information about the topic including links to other resources with more information about each.