In fact, for me, I can honestly say that OS X has almost strictly regressed in terms of my day-to-day experience. Spotlight now covers up way too much of the screen for almost no gain; if I'd wanted that, I'd have just used Alfred. Mission Control is still not as powerful and flexible as Expose + Spaces, and now it even goes so far as to hide desktop thumbnails even on my dual 27" monitor setup. Seriously?

What's most shocking to me is how much Windows has caught up from a UX perspective. I have Windows 10 on my (primarily gaming-oriented) desktop. Since I don't use the desktop for much programming, I almost never find myself wishing that it was running OS X instead. That's a real blow to the magical grip that OS X once held over me. Cortana is just as good as spotlight -- better, even -- and it manages to be much more space efficient as well. Windows Explorer is so much more useful than the bafflingly overly simplistic Finder. On Windows, if I want to tile windows, I can -- get this -- just drag them to the side, top, or any of the four corners. On OS X, I have to either fiddle with their impressively clunky split-screen full-screen app disaster or use a third-party tool like Spectacle or BetterTouchTool.

I could go on, but I'll leave it at this: there was a day where I never wanted to touch Windows again because I felt OS X was so much better. Now I find myself only really sticking to OS X for two reasons: (1) it still has better touchpad interaction on a laptop; (2) it's still based on Unix so I prefer it for programming.

You're right that there's a certain amount of rose-tinting with regards to Snow Leopard. It certainly wasn't perfect, and I wouldn't really want to switch back to it; the world has moved on since then, and SL isn't really competitive as a primary OS now.

With that said, though, my use-case in OS X hasn't dramatically changed since Snow Leopard --- mostly web-browsing, some IM, using the Terminal for various tasks --- but OS X's stability has changed in that time, for the worse. Apps crash more often, the OS itself is generally less stable and prone to random freezes which require a hard-restart. Doing a fresh install didn't fix these issues, and my fianceé's MacBook has them too, which makes me think it's not just hardware issues.

I think what I'm really looking for is Snow El Capitan: a year where nothing new is added and Apple throw intense focus on fixing the various weirdnesses that are introduced during their breakneck release cycle.

So much hideousness.

Like breaking Save As... with a clunky autosave set up.

Like a badly thought-out full screen mode that couldn't even cope with an external monitor being connected (this being something that worked on the 512k Mac).

Like automatically terminating background apps, and purging resources within apps (so that Safari would reload all your background tabs randomly).

Like App Sandboxing which is so restrictive as to rule out an entire class of applications from the piss-poor Mac App Store, and to continually fill the Console with Apple's own system services getting dinged for sandbox violations.

Like discoveryd.

Like abstracting away the filesytem, so that you hit "Move" on an document and get a crippled filepicker appearing from the title bar.

Have they actually added anything good since 10.6? Some window management has improved a bit. Startup is immensely better. iMessage is getting there (though iChat AV was still better at group video chat than anything since, including Hangouts). You mention AirDrop, but that's a mess (and the awful Chooser was still a better way of finding other Macs to connect to than the Finder is today).