Some additional observations after using Golden Gate more:
1. Golden Gate is a confusing mix of Aqua 3D, Big Sur flat, and Tahoe transparency. I like having the Aqua-ish toolbar buttons, but they appear cartoonishly large in Safari and look weird compared to the flat, lifeless URL input. Apple should add depth to elements that allow text input. If the Search bar in the Finder window has depth, there's no reason the URL input should be flat. Apple did this correctly and with subtlety up to Yosemite.
2. I really do applaud Apple for reverting to the Big Sur-style sidebar. The floating sidebar was nonsense. However, because the sidebar is so flat compared to the window to which it attaches, something seems off about the sidebar's appearance. If Apple made the traffic light buttons glassy, that might add balance to the sidebar, but I'm not sure if that's entirely the solution. Apple should consider some type of divider like in it used in Tiger.
3. I don't understand how anyone can use light mode because it is blindingly white in Tahoe on my MacBook Pro. Toolbar buttons and other parts of the UI are generally distinguishable when using dark mode.
4. I haven't a clue why Apple relies on window contents to provide colour to the UI. Apple, make a choice to use some texture and colour without relying on the background! The transparency is so lazy.
5. Apple has been accumulating a debt of bad pop notification UIs for years now. These do not seem considered at all, and because Apple is not laser-focused on macOS, these parts of the OS will continue to languish.
6. Music is a UI nightmare. Absolute rubbish. Scrap it and toss it in the dustbin.
7. Applications can still be dragged into the Finder toolbar for quick access!
8. The system is really responsive except for scrolling in the Finder with tabs open. Whatever calculations are needed to render the icons behind the transparent tabs causes very slight stutters.
9. Golden Gate is much more enjoyable than Tahoe, but it still has a long, long way to go. If Apple puts in the effort to actually consider all of the UI elements, it might find a winning combination that balances its three main main design languages. Golden Gate isn't there yet.
Edit:
10. The pill highlight in the top menubar and dropdown windows is such a tired, lazy design. I don't understand Apple's obsession with pill shapes. They cause disconnection and lag between the selection in the menu and dropdown window. It just looks weird.