Dark Mode helps enormously at making it a "distraction-free" environment; the controls and background are much less obtrusive when actually writing. It performs well, never lags out, which is a problem with many programs when I get to typing fast.
The ability to customize a theme by just changing it, and then hitting Update and having it cascade thru the file, is very nice; it's like an easier CSS.
That's about the end of the good parts.
The default blank document theme of Helvetica Neue everywhere is so bland and monotype, I can't imagine even IVE-1138 writing in this and thinking it was acceptable. I miss when software shipped with some personality, because this is not it.
Apple's spelling checker has always been wonky, but it persistently objects to the use of "their". I felt like I was having a senior moment, "is that the right way to spell a word I've used millions of times?". It is. Pages is just a broken machine.
The actual controls are inscrutable. You can find a few basic styles on the style sidebar, but for example adding a superscript? Hidden in menu Format, Font, Baseline, Use Superscript which you then toggle on, type, toggle off. No way I can see to just select text and make it a superscript. You can change text colors easily, which I would rarely want to do, but changing background, say for zebra-striping a table, is hidden under Layout.
Altering a table's size and columns was unreasonably hard. I probably wasted 15 minutes fighting with this, before just copying the tables to BBEdit (which made them tab-delimited), pasting back, and setting tabstops for an unfrozen caveman-style typewriter table.
Making a document 2-column is under Layout, but setting page margins is under the Document sidebar, so adjusting layouts takes a lot of back and forth. When setting a page footer, I hit tab thinking it'd move to the next footer tab, but instead it added a lot of space and made it impossible to change the footer under it; I had to undo until it went away.
The toolbar has a laughably small selection of tools in it, no obvious way to make something like the Word markup ribbon; say what you will about how ugly that is, it's efficient for simple formatting.
I succeeded in writing a short, fairly attractive pamphlet, but it took me twice as long as with MultiMarkdown. I think it'd be very frustrating and slow to use for a longer book.
I'll have a way to release the project pretty soon.