The VMS help system, while far less verbose than Unix man pages was, thanks to its hierarchical organisation really, well, helpful.
My basic introduction was that my boss sat me in front of a VT220 terminal and told me about the HELP command.
Later I discovered the absolute awesomeness that was VMS (at that time, OpenVMS came later) documentation.
For me and to this day it's the benchmark how documentation should be written an organized.