I have to concur, fish is simply an amazing shell for interactive sessions. I've been using it for so long, I just take some things for granted, like the incredible autocomplete. As far as I understand, it looks at paths in history entries and won't suggest them if those aren't valid in the current directory. Then you also have the "shadow suggestion" described by GP, the Alt+arrows to just complete part of a history entry, the really good Ctrl+s (which also works for commands that implement fish suggestions, not just history), and so on.
Extremely useful on a daily basis.