It really doesn't anymore.
In particular the UI became a dumpster fire. I won't go into the Playmobil interface of Big Sur, let's just say that's a question of (acquired?) taste.
However, the interface is much too big. Most of my computer screen (a 15" MBP) is taken up by empty space.
Then you have all kinds of weird behavior in Apple apps that just wasn't there before. And I'm talking "Apple apps as shipped with MacOS", in particular Safari and Mail.
If I have Mail running in full screen, Safari in full screen also (different "virtual desktop") and I click on a link in Mail it will attempt to open it in safari on the same screen as Mail. No, it won't attempt to tile the windows, just stack them. Yeah, that's not supposed to work and it doesn't. In order to get back to Safari, I have to un-fullscreen Mail. If I try to reach Safari via Expose or Mission Control or whatever it's called today, it will select it, then when the animation finishes zooming in, it instantly switches back to Mail.
Speaking of Safari, my "favorite": try to open a new tab. Wait around for an hour while it spins the beach ball. Tried removing the history, the "smart" thingies on the new tab page had already been disabled, etc. This keeps on happening from time to time.
Then for some reason, sometimes in dark mode, the active button of dialog boxes is fully white. If I click outside the window and come back, it gets its regular color so I can read the text.
Also, auto light / dark mode used to work as it says on the tin. Now it randomly doesn't and gets stuck in one mode or the other. Fun fact: if I go to settings, switch from Auto to the one it's stuck it, nothing happens. Switch back to Auto, and now it knows how to change. No, it's not timezone related, as I don't change those and haven't since 2019. The clock is always on time.
I also use a USB drive for time machine. Sometimes, for some reason, the time machine icon in the menu bar becomes white on light grey. (In Big Sur the menu bar doesn't change color in dark mode, so why does the icon even have a light mode?). In Finder, the "eject" button is not aligned with the name of the drive until I click on it. Fun side effet: I have to click it twice to actually do something useful. You might argue that aligning the icon is useful (happens after the same click) but I'd rather I didn't have to do that. Even on my dinky file manager in Linux this doesn't happen and have never seen it happen.
Then, there's the App Store. For some reason, sometimes it won't update the apps. The progress goes all the way to almost full. Then it does something for a while. Then it says it needs to close the app. I say ok. Then it says "yeah, actually, I can't update it". Why? Won't say. Then after a while, it manages to update it somehow. This has happened with multiple apps, including Numbers (Apple app).
Now all these (except for the Safari beach ball) first started happening when I updated to Big Sur. I figured my mac may have accumulated cruft or incompatible settings during the years. It's a 2013 MBP that got the "transfer your data" from my older one and it also went through a bunch of public betas. So I figured might as well try the Windows treatment and do a clean install. Nope, none of the issues went away even without copying over anything from the previous install.
So even on "Apple hardware", there still are issues. And I really don't think any of those issues can be attributed to my particular hardware being old. And all of those issues are new issues in functionality that had been in MacOS for years and that worked well.
Now my MBP is gathering dust because it's just irritating to use. I find Linux (on Arch with i3 of all things) is getting out of my way and being less of a hassle to actually get my work done. Of course, I hate the hardware (some cheap HP probook from work that rubs my wrists when I type) but sitting at a desk all day it doesn't matter since I'm not physically touching it.