It is great that we have global menu now. But it would be even better if we also had a window button widget (close, minimize, maximize) to get Unity-like experience. When window is maximized - header bar is dissapears, and window controls and menu are shown on top panel. It will free more space for content on screen.
There's a widget called "Yet another window control" (or sth like that) on the KDE Store.
We even have a 1st party widget for that now.