In general designers talk about UI in terms of ”good” and ”bad”. MacOS having amazing interfaces (maybe not) and Android is horrible.
But if we abstract from those simple terms and look deeper – the working design is one where each element is brining the value.
And it does not matter which color and size are used. In great design each element has a purpose and a reason. It will be easy to describe what element are doing and what value are brining. We should aspire to keep only trully important in the UI.
Each element: border around the text, buttons, fields, pop-up, dash, icon or input are brining a message to the interface. And by removing those small bits of unnecessary information we can make the main action more prominent and easier to use.
The best interface is the one which you don’t need to use.