I did one project in Drupal. What a heaping pile of shit unfit for any actual developer and not someone's wife who moonlights as a small-business homepage developer. Never again.
Drupal 6 was actually a pretty consistent hooks-based system that exploited the fact that PHP has a fast and feature-rich implementation of the function lookup table.
Drupal 7 started the migration to object-oriented code and was halfway through the messy rewrite when it was released. Drupal 8 finished where Drupal 7 left. That's where the majority of the developers left as well (pun intended).
