The game changer for me was the detailed mode ("H"), which makes ed a lot more pleasant to use. I wish it could be passed on the command line as an option and aliased in the shell... maybe I should patch it.
I've started to find ed surprisingly fun to use for quick edits, I'm not leaving nvi yet but it has this nice "ancient Unix" vibe.
It would take very little to make it very good:
- a quick shortcut to open the file at current line in a pager
- perhaps redesign it to work without having to hit enter after you give a command