I never would have thought that this dialog box would be quite so polarizing.
I tend to fall on the 'don't like it' side, primarily because it is too busy. It is difficult to get aesthetic spacing (for me, tight) with all the panels. I use the edit field parts (standard and custom) far more often than I use cover or format editing, and would prefer to have both standard and custom metadata on the same page.
I have been considering redoing it to use three tabs (fields, cover, formats), then submitting to Kovid to see what he thinks. I may still...