AmigaOS.... actually, it's hard to fault it ^^

Memory protection perhaps?

How about Plan 9's user friendliness? XD

I didn't find it hard, just very far from anything else that can be offered.

Well yeah I use it! But most people wouldn't be able to get it to boot.

Yes, that is true.

XD

System/370 is worse, though.

ITS and its user friendliness and security.

TOPS-20 and the verbosity of its commands. (Want to know your disk space/usage? On Linux and UNIX: df On TOPS-20? INFORMATION (ABOUT) DISK-USAGE (OF DIRECTORY))

UNIX (and its relatives) and the intuitiveness of its commands. ("I need to type a file out onto my screen, I know I'll call that program cat!")