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.
When I accidentally download a file on my phone, I actually have no idea where it went, it just kind of vanishes into the aether after the notification disappears
One thing I always liked about Blackberries aside from the physical keyboard was the scroll wheel. People joke about them but they worked really well and smoothly (before the actual ball got replaced with a bullshit push sensor round about 2009 or so) and you could dial in on a specific pixel easily - something you just can't do with a touchscreen - which made the tiny screens a lot more practical than they otherwise would have been.