Well, most improvements are internally.
- NewIcons and DefIcons are now integrated in a system-friendly way.
- Workbench has an Arexx interface.
- You can arrange icons in a window by name.
- icon.library has some nice new functions making patches like PowerIcons (truecolor png icons) possible.
- system programs (prefs, tools etc.) look a little bit more modern.
- there is real 64bit support for the internal IDE bus (note: with the original scsi.device you still have an 8GB limit, even with SFS !)
- datatypes have support for multi-image files (e.g. multi-page TIFs or GIF-Animations)
- some multimedia utilities (movie player, mp3 player) are now intergrated into the os. (Earlier you had to test several products and to choose one of them, this decision has been made for you now
)
- probably some others that I don't remember because It's so long ago I used 3.0.