Linux kicks ass in certain areas, embedded, servers, HPCs, its just not a great desktop.
It is too a great desktop, I've been using it as such for, oh, 15 years now. It has just one thing going against it: it's not Windows. That means 1. little Johnny from next door can't help you out when you screw things up, and 2. it won't run Windows applications (at least not well), so it's not easy to exchange documents between you and people who do use Windows.
If there was only Linux on the desktop, people would be just as happy with it as they are with Windows. But it's a Windows world, so you might as well go with the flow and use it too, and there's nothing wrong with that.
But I maintain that from a pure usability viewpoint Linux-on-the-desktop is just fine.
(Caveat: talking about the classic Gnome 2/Windows 7-like interface. Haven't used Unity or Windows 8 for any length of time, and not planning to.)