AmigaOS was, overall, the best OS I have ever used. As little technical as possible, but as much as needed. It was an OS, that would gently make you a power-user. I am not going to rant, but my God, was that a good OS! 10 years ahead of its time!
It felt like it was so "feature complete" even around 1990. Add a web browser (and networking )and run it on a modern spec machine and I'm sure it would be perfectly usable.