Memory compression in Mavericks was also something I feel is great. Although I never dealt with it directly as a programmer, only a user.
The problem Apple has is that the early-2015 Macbook Pro Retina's really hit the balance point with the physical form factor. Enough heft to feel solid without too much weight. Enough battery life to do real work. A solid set of ports: HDMI. Magsafe. USB 3.0 ports. A keyboard that doesn't break due to random micron-sized dust particles.
So, a LOT of people want a 2015 Macbook Pro but with ONLY the tweaks to bring it forward to 2019 technically (memory, CPU, display, change to the two Thunderbolt 2 connectors to USB-C Thunderbolt 3) while leaving it in 2015 physically.
The marketplace has become much more competitive as innovation has pretty much stalled.
I'm thinking of moving back to Mac OS after being on Windows for the last six years.
On the software side: slowness but more importantly a general decrease of opinionated cohesion, and an increase in odd UX decisions. Facetime calls to my iPhone trigger alerts on all of my devices, even if I'd prefer it to just be my phone (I rarely use Facetime on my machine). Beyond that, there are too many useless popups that interrupt me in what I'm doing that I have to X out of that I end up with a screen that looks like the topic post -- hence the pejorative "10.15 Vista" which is how a lot of folks about Windows Vista when it was released after the relatively sleek and polished UX of Windows 2000 and XP.
2. Open the Preferences menu.
3. De-select the "Calls from iPhone" checkbox.
4. Done.