I wouldn't go as far as calling it a horror show, but do find it genuinely unpleasant to use. In a default configuration GNOME's task switcher seems to assume that there is only one window open for each application. Switching between multiple windows in the same application is rather inconvenient. The title bar stuffs in frequently accessed options then hides the menu bar under the hamburger icon. Those frequently used options are the ones I am least likely to access from the title bar since they are bound to hotkeys that are common to most programs.
For anyone who is accustomed to other metaphors, I'm not terribly surprised by the description horror show. Even as someone who is willing to adapt to change, many of the changes seem to be contrary to usability or efficiency.
GNOME's task switcher has two modes, the one you're using switches between applications. Alt+(the key above tab) switches between windows within an application.
The hamburger menu keeps the applications looking clean, if there's anything I use that frequently I'll just use the keyboard shortcut.
It's improving every release, but if you want traditional, I'd choose XFCE.
I would far prefer an organized UI to one that tries to look clean by tucking away functionality under a hamburger icon.
This is not to say that I insist upon menus. Since I never had much invested in Microsoft Office, I do appreciate the ribbon bar. It does a fairly good job of organizing and exposing functionality in an otherwise complex piece of software. Contrast that with GNOME's approach. It is rather difficult to design a complex piece of software when most of the functionality is hidden behind a single menu.
At the other extreme, you have software that is somehow command driven. The interface can be kept clean by hiding away all of the functionality. (An example of this would be vim.) Yet that is not what GNOME is trying to provide. GNOME is a graphical interface that is supposed to facilitate discoverability. Discoverability will always be a trade-off between visual clutter or a reduced feature set. The only other option is to hide functionality, which is dangerous in a GUI.
A "clean" UI is often a less functional or efficient UI; cleanliness is usually achieved by adding indirection or removing functionality. But Gtk3 isn't even clean; it's often cluttered. Just look at the title bar on dconf-editor when you're 5 levels deep in a config tree.
Menus are ideal for commands which are individually infrequently used, but collectively frequently used. That is, where any given menu item isn't used often enough to warrant learning the keyboard shortcut (not that Gtk3 menus show shortcuts, because they don't), but the menu as a total is visited to execute a command frequently. Consider things like IDEs, photo manipulation, video editing, sound editing, basically anything with a lot of tools to apply.
I find it particularly ironic that Gimp - the OG Gtk - doesn't use a hamburger menu, because that would be ludicrous.
Another point with menus is that the typical top-of-the screen, and nowadays "hamburger" menu is just dumping ground for all functionality, and should be at most of a secondary use to common and context-specific actions represented by buttons/context menus/etc.
