Developer of Pathologic [1] here. Code-wise, D8 is really a whole new paradigm for the system, so if you've given Drupal a look in the past and rolled your eyes at the PHP 4-ness of it all, I really encourage you to give it another look with fresh eyes in the future.

In terms of user-facing features, I think the greatly improved support for multilingual sites is the most exciting new feature (especially as just this week I've been encountering headaches related to i18n implementation on a D7 site… argh).

1: https://www.drupal.org/project/pathologic