- macOS used to follow very consistent UI guidelines. Now Apple's applications are all over the place. It gets even worse with Catalyst.
- Stagnation of the development of low-level features. Where is the equivalent of user namespaces, container facilities?
- Invention of their own graphics standards, which makes life for scientific computing hard. Apple used to be a relatively good citizen, supporting OpenGL, proposing OpenCL. Now we have Metal. Which may be great for games and uniformity with iOS. But scientific computing has settled on CUDA, OpenCL, and ROCm. Apple supports none of these technologies. (Imagine being able to hook up an eGPU and experiment with some neural networks before doing the heavy work on a server.)
- Since several versions PDFKit (such as Preview) applications have become very unreliable. E.g. you used to be able to regenerate LaTeX files with the PDF open in Preview and it would just rerender the PDF. Now it crashes a lot of times.
- macOS has introduced notification center, but there is no option to turn it off, besides changing the do not disturb time period from e.g. 9:00 to 8:59.
- Catalina introduces a read-only system volume. In principle this is ok, but they have made it so that you have to jump through hoops if you have something that installs into a top-level directory (e.g. a package manager). You have to use a new configuration mechanism that creates a folder that only exists virtually, reboot, create an APFS volume and edit fstab to mount it automatically.
- Notarization, which gives Apple even more control over what gets run on macOS. Yes, I know that you can circumvent it, but that's not what many users will do. So, before I could just sign my Qt app, now I have to run it through Apple and set up a command-line workflow to do it.
- Applications trail iOS versions. E.g. Messages only has a subset of the features of iOS Messages.
- Dropping applications that users have developed workflows around. E.g. Aperture, the original iWork (for years, the new iWork based on the iOS version did not support features such as linked text boxes).
- Breaking Safari extensions for the second time (in Catalina the Safari extension gallery is not supported anymore). No more uBlock, vimmy, etc.
Disclaimer: used OS X from 2007. I am not claiming it is all bad. But I think macOS has more and more become a consumer platform and has become significantly worse for developers, scientists, etc.
