Command left/right arrow, for example, switches between terminal windows in different spaces, and to terminal windows within the same space as well. Press the shift key as well to shift between tabs. (At least on my MacBook Pro's Japanese keyboard.) I don't recall have modded this behavior.

That's definitely better than command-`, thanks.

It's still not as nice as alt-tab, though. Frequently most of my windows are a mix of terminals and browser windows. I may be using several web apps and several command-line tools. Having to think about whether the application I want to switch to happens to be using the same "shell" application is not helpful.

I just want to be able to use one key to cycle through all windows in all spaces, and which lets me easily flip between the two most recent windows. Windows (and virtually every Linux DE) has had this for decades. It amazes me that macOS only recently got this, and only because of a third-party tool.

Yes, Alt-Tab is a HUGE improvement over Apple's implementation because it not only restores minimized apps as it should, but can also create a window for a running app that lacks one (with Finder being a critical example).

Hold option as you release cmd and it will behave as you describe (opening the default window for an app with no open windows, restoring minimized apps… it’s equivalent to clicking the Dock icon for that app)