You could make fully bootable backups of your main drive just by copying everything from the root to a new drive. None of this re-installation rubbish or ownership getting messed up or what have you. It even worked across architectures, a Mac System 7.5 installation will boot on both 68k machines and supported PowerPC systems, just swap the drive over and you're going.
It would be nice to use a desktop environment that's inspired by the classic Mac interface (I particularly have a soft spot for the Platinum theme), but without an ecosystem of applications that conform to the Macintosh User Interface Guidelines, then all we have is yet another window manager.
It's the ecosystem of applications, like Microsoft Word 5.1, Adobe Photoshop, Adobe PageMaker, ClarisWorks, and others, combined with the Mac interface, that made the Mac so special.
Also, if you like copy/pasted Linux apps, there is the `AppImage` project that provides such a format and its tooling is rapidly improving. It is a self-contained alternative to Snap and Flatpak which only handle the file container and leaves security/sandboxing and distribution to other projects.
But yes, the classic Mac was the first computer I ever used and I also have a sweet spot for it. I still own some recent Mac, but don't really like the increasing lack of flexibility and non-iOS development environment macOS has and do all my development on Linux. Classic macOS was the ultimate flexible OS, you could monkey-patch everything (which is also called a virus, but... POWER!).
Disclaimer: I am one of the authors of AwesomeWM, a Lua window manager framework for Linux.
But it won't boot.
If you have the proper bootloader in place it will boot. This is less the fault of Linux and more that x86 platform have to boot multiple OSes.
A Raspberry Pi for example will happily boot from a .tar.xz archive.
What I miss the most is the true spacial Finder. Copy a file to a floppy disk, add a custom icon and place it at a precise location on a window. Go to a different Mac and insert the drive. All those attributes are honored. Every single time no matter what. Such a simple and powerful model.
(And honestly, while I see the advantages, I'd rather we not have this feature so we can also not have .DS_Store files. .DS_Store files suck.)
There used to be a one to one mapping of folders to windows. The moment you decide 2 windows can show the content of the same folder simultaneously (which has its advantages), you run in these issues. Which is the canonical view that should be preserved?
And yes, we had all that without . DS_Store files.
I'd posit most of us rarely open the same folder in two different windows, which means the icons should behave as expected in all but an uncommon edge case. It has worked in my experience, at least.
But separately, just as a though experiment: when an icon is moved in one window, the placement ought to update in both windows, in real time. Probably wouldn't have been feasible when macOS X was new, but perfectly doable today given modern computing power.