The Way Drupal Theming Was
When I started Drupal theming in 2004, it was all a bit overwhelming. Back then, the core theme engine was something called Xtemplate, and it gave the impression to the n00b themer of being a great big mess. When you looked at the page template, it was one big blob of markup and logic, and it was very hard to figure out to change just about anything. What's more, it seemed to be very brittle: change something and you got the white screen of death.
And thus life was for the themer through Drupal 4.5 and the beginnings of 4.6.
New Drupal Theming Power
Then, in 2005, came the PHPTemplate theme engine, thanks to Adrian Rossouw (now with Development Seed), and the heavens opened up.