Gave 3.3 a quick test with high hopes. Created a simple post using TwentySeventeen theme. Stacked a title, image, and 2 paragraphs. Looked very good in the editor. Pressed "Preview." The layout changed, the typeface changed, the type size changed. Part of image overlapped the theme's sidebar. Looked like crap with no ready way to fix. Come on folks. This was a very basic test and it utterly failed.