It's quite usable for casual users who don't know the names of the applications and want to explore what's in the computer. KDE offers a gret solution for this; in the start menu applications are organized by category and there's a short description next to the icon explaining what it does.

If you enter a category it doesn't add a layer, it shows the applications in the same view as if you were opening a folder; and at the bottom you always have a Search bar which works great and power users can comfortably use.

So, say, you want an application to play video. You go to Applications, select the Multimedia category, and click on the icon that says "Video player".

Both Unity and Gnome3 also have solutions in which you don't have to compromise or use quirky macros to get the behaviour you want. You can have the best of both worlds. But then, as usual, many will continue bashing Linux GUIs as if they were a usability nightmare and totally inferior. C'est la vie.