To this day, it lacks or struggles with very basic things, like interactive dialogs, toolbars, tabbed interface, file system navigation, etc., etc. So Emacs does 5% or what an editor should do quite will, and is surprisingly under-powered and old fashioned at the other 95%. Unfortunately, it didn't keep up with the times and fails to take advantage of the entire world of GUI design that's revolutionized computer science since then. In fairness to Emacs, its original design was conceived in that context and is rather good at some things, like flexible ability to bind commands to keyboard shortcuts.

User interface is terrible I was using Emacs in the early 1980's, before there were GUIs.