Was thinking about this the other day, while talking to a friend of mine.
What parts of the amiga OS were good ideas that hold up today?
Some things that came to mind (big and small):
Generally being able to replace and swap out parts of the system (allowing for things like Dopus and the various workbench replacement stuff)
Being able to run efficiently on very limited hardware
Using plain terms for as much as possible of the system commands, folders etc
Extremely well documented software and hardware
Applications being able to interact with each other through arexx (well, more or less)
Multiview
Always thought tooltypes and datatypes were good ideas. Im sure there's drawbacks as well but that could be more specific implementation than anything else.