It was good because it was both Opinionated (in other words, the path to write software that follows the design was easy, and the paths to write software that violated the design were hard), and also well-researched by human interface experts.
Now what we appear to have is "someone's opinion" design. A bunch of artists decided their portfolios were a little light and they needed to get their paintbrushes out to do something. I don't work at Apple, but my guess is that their HI area slowly morphed from actual HCI experts into an art department, yet retained their power as experts in machine interaction.
So here we are, we still have Opinionated design, but it might just be based on some VP's vibes rather than research.
