@Shufei The problem is that - from what I hear, confirmed by personal experience - GNU/Linux has kinda abandoned the UNIX philosophy of small, simple programs that do only a couple of things and do them well.
I see someone already suggested you try out the *BSDs, and I can only agree: my experience with OpenBSD has so far been quite enjoyable (though beware of the limited number of supported filesystems!)
I seem to remember an alternate command to man that did show more human readable intros. I can't recall the name, though, nor speak to its coverage.
There was also someone on gopher who did their own note-taking on commands. I think they wrote a script called mman (my-man) where they kept notes and tricks and stuff.