Hi Courtney!
Groups/columns and the accessibility changes are top of mind. Really enjoying those. The new writing view is nice, too.
Biggest point of pain right now is the arrangement and handling of metaboxes. Building complex custom sites often means making use of a variety of plugins and fields (usually with the Advanced Custom Fields plugin). Plugins like Yoast SEO have added their own settings-style sidebars which is helpful, but is going to quickly get out of hand as more plugins follow this paradigm. It’s also a very cramped space to add anything but the simplest user input.
I’d love to see some solutions that provide developers with ways to fit in meta content like this outside of the Gutenberg block experience, but still within the editor. BTW, this may already exist and I just don’t know about it.