The level of polish, robustness, ease-of-use and efficiency of today's KDE versions is incredible. It is lightweight, too. This is the desktop environment that stays out of the way, but here when you need it. There are no strong decisions that surprises anyone, things are familiar, there is no hostility towards users requesting obvious features. The user interface does not change so much from versions to versions, but is rather improved (a lot, in tiny ways).
Only, it is secretly so. Nobody seem to know. I don't know what can be done about this.
KRunner is doubly affected by this. It is not quite discoverable, does not get in the way of users not using it, yet is so convenient. I'm lost whenever I'm using another environment just because KRunner is not here.
(it can also be brought up by alt+space, which matches the keys of Launchpad on Macs)
KDE 4 was pretty messy - from instability to questionable features or lack of features - 4.0 "released" too early, nepomuk (and later baloo) being a resource hog, the PIM suite pulling in two database servers, amarok only supporting fuzzy filters, virtual desktop support stagnating in favor of "activities", kwin compositing had lots of glitches. Even krunner used to crash or hang frequently. I still have ~/.p script to quickly kill and restart plasma (via krunner, hah) from those days because it would fuck up so often.
Really glad that they spend the time since then motly polishing and KDE 5 has been much better about not shoving unwanted crap down users throats.
For Windows, this can be accomplished with PowerToys Run. It's effectively replaced my Start menu for 99% of things.
Alternatively if I type 'hacker', I shall be shown the three windows I currently have open, along with the 7 bookmarks, that match that string.
Otherwise it's a handy shortcut to launch any application I know is installed on the local host.
I believe it's consistently been providing this service for more than twenty years.
Compare ctrl-escape on Microsoft Windows, which should offer much the same experience.
Often while using Microsoft Windows I am trying to find a way back to a fleeting pop-up that graced a corner of my screen before I could fully read or act upon it. This invariably fails to provide a sensible result. For example, type 'update' if you wish to search for, but certainly not find, the source of the various noisy 'Windows Update' notifications. Prepare thyself for disappointment.*