I downloaded and started to explore the beta last night. Obviously the core team puts a lot of work in each update and/or new version that gets released, so you have to appreciate the fact doing this involves a lot.There will always be elements that some like while others not so much, but as I test this version out, I will do it in the mind of typical user and not as a theme developer.

There are some things though that makes me scratch my head wondering, why? As Jeff mentioned about some may see strange things happening when suddenly something turns into a list, or something else happens as they type in the post editor. Even the site icon (which really should have been named "favicon") may create some confusion, albeit I am sure many will be happy they can add a favicon.

Regarding the Customizer, I personally believe this should have been left strictly for "theme options" only and to leave out "admin" functions out. But I know the customizer is a heated topic so I will leave that one alone.

I will continue to explore and test out this beta today and see how things go.