I couldn't wait for global menu and now there it is, finally . However in the corner of my mind I "expected" it won't be well thought out, as it is usually with first releases and I was right. Now to the point(s): 1. Global menu panel or actually a widget in the panel has no fixed sizes. In result, it's dynamically generated as it is needed. The problem arises when I want to put other widgets as system tray, clock, etc. They don't hold their position and after reboot they jump to the left and then again to the right when new menus are generated. This is a mess. Menus never take the whole screen width so the space is wasted if we can't add more functionality to the panel.
It is nowadays quite popular to have two standard desktop setups: a) with normal panel b) with dock. Second case would allow us to create sort of unity or OS X setup, but in face of current plasma's global menus shortcomings, we just can't.
The point is: menu widget should get fixed, adjustable size. EDIT: Someone on kde irc channel pointed me to the panel separator. Never needed it before so I always ignored it and forgot it's even there. Anyway, this separator seems to fix the issue of moving other widgets. Case closed
2. Menu panel doesn't work with all programs, mainly with gtk ones (firefox, gimp). I guess that's too hard to implement global menus across toolkits, because unity panel suffers from the same issue, although qt programs have problem working with it there. Well, I can live with it, but maybe, MAYBE in the future there will be a way to improve it somehow (I'm a dreamer ;p), just a thought.
3. Global menu widget should not only have fixed and adjustable size, it should be possible to set it's place within panel.
Imagine unity alike setup with a dock on the left. It looks way better to move menus to the border of the dock, where the opened window may have its left border. With completely transparent menu it can be done by simply shortening the menu panel on one side, but what if you use more traditional, coloured panels? Shortening panel would create a bad visual effect. Having full width panel with menu widget in a slightly adjusted position - that would look really well. Please, allow us to do that. The point is: make menu widget be able to have fixed place within panel so it could be moved and set in various positions.
4. Let's talk about focus methods. With click-focus, global menu is ok. However my preferred setting is when focus follows mouse. I know I'm not the only one who chooses windows focus to behave that way. At the moment I have to move my cursor very fast to the panel to hold the same menu. It's annoying and it's unpractical. In unity it can be solved easily by setting that allow menus to be shown in title bar in un-maximized state, and in panel in maximized state.
Moreover, even with click to focus, moving mouse all the way to the panel is unpractical. Panel is great only in maximized mode, so having alternative in title bar at the same time would solve the issue.
The point is: allow for having both: panel and title bar menus. This way an awesome focus follow mouse mode would work finally correct with global menus.
5. This leads us to the next point: strip and merge title bar with global menus in maximized mode. Yeah, we can use a script to un-decorate windows of title bar in maximized mode, that's what I do now. However this is not a desirable method, because script has some flaws and doesn't work perfectly and also we loose access to window buttons or other functional icons we may adjusted to it. Sure, I do have access to them on right click on icon task widget, but that's not so easy and productive method to access them.
Again, the whole panel is too big for menus, so adding windows buttons to it in maximized mode would help a lot. The point is: create setting to merge title bar buttons with menu widget in maximized mode. 6. This point is rather a bug fix. I saw on few plasma 5.9 neon reviews and some didn't have title bar menu icon, because this setting wasn't working. I'm on Manjaro KDE and after upgrade, I have exactly the same bug. I did set icon on a title bar and set it to show there and... nothing. It's not showing. Panel menu option works, but window bar menu doesn't (and I know they are excluding each other at the moment, I checked both settings). EDIT: I found out that the menu icon works ONLY WITH BREEZE window decoration. Does it means that all old window decorations must be updated or is there a way to make it work with older custom window decorations?
The point is: menu icon on title bar is bugged and not showing after upgrade to plasma 5.9.2. I am not only one with that problem so this needs to be fixed. 7. Why menus must be clicked and clicked again and again each time we move to the next node on the menu? Why won't they open automatically when following mouse when first one is opened, just like you can do with for example with firefox menu or libre office menu and so on?
The point is: make menus follow mouse and open automatically once one of them is opened. 8. Menus should disappear when their window is minimized.
Without those many fine tunings, current menu bar is hardly usable. I am thrilled it is finally there, but I hope that in the future, it will gain in functionality and become very flexible and versatile tool to set up our desktop just as we like it - kde rocks!
Here is my current setup that I came after many trial and errors (had to keep system tray in the dock, because it's not working well with menu panel at the moment, but I would prefer to make full unity alike setup):
By the way GTK applications do not have menu button even when it is enabled and when all the dependencies and tweaks are done to enable global menu in gtk applications. At the same time menu button appears in Qt applications.
After trying the Global Menu, I find 3 points that can be important
1. What is mentioned in the michaldybczak post in point 7
make menus follow mouse and open automatically once one of them is opened.
2. Some programs do not work like the case of Vym (view your mind) an interesting mind map program
3. When I use Unity I find it very easy to see the name of the document in the same space as the global menu. The document name is shown by default and only when I drag the mouse over the area, the menu is displayed. It seems simple, but it is very comfortable. Especially when you have configured your kde, with the option "no border"