Sliders with value display
Displaying the range of values is very useful thing. Sliders allow users to view and select a value more clearly, it's especially useful for adjusting settings.
At the moment in GNOME, all sliders have to be "adjusted by eye", this is quite inconvenient. Plus, when you resize the window, the size of the slider also decreases. Adding a value displaying for the slider adjusting will have a very positive impact, at least, there will be an opportunity to make more precise adjustments.
Example from Material Design HIG:
Example from Windows: