I've been using the venerable ubuntu 14.04 LTS with plasma 4.13 for quite some time but finally upgraded to 16.04 with plasma 5.5. The shock, the horror... I know it is not the latest version, but please bear with me. I was not at all pleased that all my colour and decorations settings were lost and I had to reconfigure them again, but ok, I've done it. I was not at all pleased that while I was setting it up systemsettings crashed every 3-4 screen changes, but this will be fixed ...right? But the thing which irks me most is that I found no way to reset the application launcher to classic menu, and that that while I disabled all video effects in system settings the launcher ignores it and still annoys me with all sorts of sliding and fading pointless artificial slowness. My main question is: is there a way to replace the launcher abomination with classic 3.5 menu? Or is it finally goodbye KDE? - yes, it is that important for me.

Also: when mucking around with panel settings it is surprisingly easy to put task manager on top of the application launcher which makes the launcher unclickable, and I found no way to fix it other than removing the panel and starting all over again.

Found the menu - in the alternatives. Still cannot figure out how to turn off animations though.

Have you investigated the animations settings for the Application Style? In System Settings -> Application Style, where you select the Widget style hit Configure... . There should be an Animations tab where you can turn off the animations used by e.g. menus, etc. There's also some stuff under the Fine Tuning tab of the Application Style dialog; I'm not sure what the Graphical effects selection affects, but probably more animations and such.

System Settings -> Display and Monitor -> Compositor -> Animation Speed allows you to affect the menu slide animation speed.

Or just disable the "Sliding popups" effect in System Settings -> Desktop Behavior -> Desktop Effects.

Same question.
Any chance to get classic start menu for KDE?
Something like KDE3.5-menu?
Thanks.

Right-click on the application launcher button and select Alternatives. There you can select between different application launchers which should include the Application Dashboard (full-screen launcher), Application Launcher (Plasma 4.x-style window with tabs and in-window display of categories) and Application Menu (cascading menu launcher with a column for favorite applications)