The UI change in the preview, i think, ends up causing more confusion and questions then it helps on focusing on what Gutenberg might bring to the basic content editing experance.

I end up wondering how this plays with custom meta and various tools that share the post edit screen. It doesn't make clear how all this would be delineated. I understand that the preview is just focusing on the main content editor but by removing all familiar UI I think it separates it a little too much.

In terms of the editor itself I was relatively happy. I think some clients who have a tendency to poorly format content will appreciate the restrain the editor brings in. Both in how it visualizes content blocks and limits the number of options.

I assume, i hope, that their will be control over removing or adding content block types (at least as a way of removing the new additions or adding in short code options). The new additions that seem short code inspired (forgot to check the output to see if thats what it is doing) should go. Especially the button and cover element. It's not clear what purpose it serves. It's really something that should be left to theme and plugin developers to choose. If they are just a preview to what could be added as a custom element then i apologize, and like the idea.

I would also love to see the content blocks more easily rearrangeable, replacing the up and down arrows with a simpler drag and drop. It should also be easier to add a new content block underneath and existing block anywhere in the stack.