The current one here (v7.5.2) really s...addens me.
Why? Well,
1. it comes as a "dialog" that is not draggable, so it stubbornly hides the content behind it.
2. it is not resizable horizontally. This is fun with tables and such it wastes more than half of my 24"'s screen width.
3. it is not resizable upwards and it is placed centered so it wastes about a quarter to a third of my 24"'s screen height.
4. if it is resized downwards and the comment happens to be a bit more extensive two vertical scroll bars appear side by side (one for the "dialog", one for the Comment text field) which already has been considered to be terrible UI design a few decades ago.
5. If I'd like to write:
TIAA – This Is An Acronym ... all capitals in bold (just to be sure, don't know yet if it's going to work here or not)
it works in the Visual editor first but as soon as I save it becomes:
TIAA – *T*his *I*s *A*n *A*cronym ... literally
After realizing that I apparently cannot format parts of a word (which have no subsequent space) I inserted zero-width spaces using the numerical entity {{​}} at the according places to simulate such without visual representation. This worked...temporarily. After a few switches between Visual and Text mode at the next edit they were suddenly and silently removed altogether.
Have you ever visited any of the Stack Exchange sites and realized how they superbly present in-page editing including dynamic preview there?