KDE 5 is fine, doing a few changes like disabling plasma volume and starting KMix at startup instead. Still have to use pavucontrol occasionally, though.
Yesterday I discovered you can switch the menu style (right click -> alternatives) to a more classic type (like KDE 3, plus favorites), or to a full screen win8 type (for tablets).
I think, they'll be available in that Alternatives-menu then. If not, you can add them through Add Widgets.
Plasma treats everything as either a widget(/"Plasmoid") or as a panel. So, you also have to have your widgets unlocked for all of this to work (including the Alternatives-menu).
[1]: https://store.kde.org/p/1169537/ [2]: https://store.kde.org/p/1160672
KDE 5, last I tried, was still missing some features and had troubles with panel positioning on multi-monitor setups. It is also missing all the little touches that made KDE 3/4 so pleasant to work with, such as Ctrl-U to clear a field (lifted right from Emacs). I stick with KDE 4 on CentOS.