Though they were a step down from Kaleidoscope schemes and appearance manager themes in terms of what they could do, those early OS X themes remain some of the nicest looking, highest fidelity themes on any platform. In particular, those made by Max Rudberg[0] hold a special place in my heart.
Modern theming systems have high DPI support which is in theory an upgrade, but the desktop appearance zeitgeist has skewed so flat and dull that the extra pixels make no material difference.