My parents did fine with Linux. My mom still does; it's certainly less maintenance effort from me than Windows would require.

It was fine for non-technical users since at least early GNOME 2, if you're ready to help them set up and maintain. Semi-technical users (Windows power users, gamers, &c — people who like to install and configure things, but fear the deep dark abyss of the terminal) were and remain more problematic.

Unity days were the nadir of linux desktop ux — it was when Gnome 2 was gone, and 3 not yet there. Still better than contemporaneous Windows 8, though.