I found and loved admin menu module during Drupal 6 ages.
This module became so popular and I was sure that it will be included in Drupal 7 core.
The main strong point of admin menu that we can open any level of Drupal admin in one click.
But now I can see that admin menu is not even in Drupal 8 core.
I'm sure that it is sufficient reason to include it in Drupal core.