What I love most about Drupal is the community. It's vital, supportive, collaborative. Competitors work together quite closely, because they understand that they achieve more this way than as lone fighters.
Drupal was one of the first CMS allowing for accessible editorial tasks. After constant enhancements, accessibility and usability today are part of the strategic development objectives. I learned to love Drupal much for the possibilty to build individual usability enhancements on project level.