Intense nostalgia. I remember my updating my MacBook from Tiger to Leopard and being inthralled with the new OS welcome video. It was a powerful feeling like a genuine leap was made after rebooting and new powers unlocked. 10.3 used Rokysopp's Eple, and I still love that song and album.

Looking back at the 10.4-10.7 era, I really miss those app icons, they were so easy to tell apart from each other just from shape. The rest of the design language was also a marvel in usability, it was so clear what everything was and how to interact with it.