When I updated to 10.8 Mountain Lion, I gained Messages (iMessage desktop) and Notes, but I lost Web Sharing. Now I have to install Apache myself, and it often breaks when I update the OS.
I updated to 10.9 when I got a 2014 Retina 15" MBP. Then I lost the ability to sync Notes and Safari Bookmarks to my iPhone over USB (I don't use iCloud). iTunes 11 broke the browser view, so I still downgrade to iTunes 10.6.3 (even on Mac OS 10.13).
I updated to El Capitan 10.11 when I upgraded my SSD from 512GB to a 2TB SSPOLARIS. That's when the redesigned Finder really hit me, and I've never been comfortable with it. There's a lag when creating a new folder and typing the name, which often means I get "untitled folder" and start navigating to another folder. The redesign of iCal pushed me towards an old version of BusyCal, and I have to use a locally-hosted calendar server. I lost Calendar USB sync to my iPhone.
I needed High Sierra 10.13 when I upgraded my SSD again to a 4TB Sabrent Rocket, to use the NVME driver. It was quite some effort to avoid using APFS. I want to be able to mount my SSD over Target Disk Mode if/when things go wrong.
As far as I know, the latest versions of Music (no longer iTunes) don't even support syncing apps. I also heard some bad things about Time Machine.
The main reasons I like Mac + iPhone are:
Mac: MagSafe, AppleScript, Office
Both: iSync USB, Mail, Contacts, Calendar, Music, Bookmarks, Photos, Wiki2Touch, Skype
iPhone: MyWi, Re-restore, Jailbreak, PHP/lighttpd
The things I lack on iPhone are: SD card reader, USB host with drivers (mount someone else's phone), Removable battery (but Third Rail case is good). No Android phone has tried to address these, and most have obscenely large screens (I like the 3.5" on my iPhone 4S).
I've had to use Windows 10 at work for the last month, but it's unpleasant. Put a folder in the Recycle Bin and want to recover one file? Nope, you have to restore the whole folder, copy out that file, and delete it again. Scrolling Excel on a Dell Precision 7550? The screen glitches out with black bars. Type accented characters like é? Only with charmap.exe, slowly. Safely remove USB? Multiple presses. I made a lot of AutoHotKey scripts, but it's a struggle. So I'm not changing to Windows any time soon, but I'm disappointed in the way Apple has gone, and wish that Linux might one day catch up to Snow Leopard levels of usability and design.