A real keyboard and general tactile-oriented inputs. Touchscreens are okay as a supplement like in the DS or Samsung devices that have a pen, but touch-centered everything has never stopped being a frustrating user experience. Even worse is the way companies have embraced it for business use as well. Heavy industrial machinery should not come equipped with unintuitive little interfaces that are clearly an afterthought at best.
The other thing is the general desktop metaphors, and file/folder structure. The way that Android, and so many apps, hide the file system from the end user just leads to more confusion when the user needs to use a file manager to track down where those apps have actually stored data only to (maybe) find them in the most pointlessly obscure locations.
As a basic end-user I have not been too happy with my experience with flatpaks. I do appreciate that I can easily setup and start using it regardless of what distro I’m using. But based on standard usage using whatever default gui “app store” frontends that usually come with distros, it tends to be significantly slower than apt, for instance, and there seems to be connection problems to the repos pretty often as well.