@The ho hum nick - Actually, 10.4 was very different from 10.3. Among about 200 other smaller things, the additions of spotlight, expose, and dashboard were huge. Kind of like how Vista adds the spotlight clone, expose clone, and dashboard clone... But anyway, here's Apple's list of the 200ish new features that were added in the upgrade from 10.3 to 10.4 - http://www.apple.com/macosx/newfeatures/over200.html Admittedly, some of the features listed are more significant than others, but they can't all be winners.
As for the differences between the other versions, I didn't own a Mac at the time, so I'm not entirely sure, but I'd suspect that there were similar levels of improvement between them. I know for a fact that there was a GUI change between 10.2 and 10.3, not as drastic as the change between XP and Vista (more like between XP and 2003 server), and the bundled apps (like Mail.app) have been constantly improving.
As for the differences between the other versions, I didn't own a Mac at the time, so I'm not entirely sure, but I'd suspect that there were similar levels of improvement between them. I know for a fact that there was a GUI change between 10.2 and 10.3, not as drastic as the change between XP and Vista (more like between XP and 2003 server), and the bundled apps (like Mail.app) have been constantly improving.