This blog is updated daily..
A general description is here.
Help in base and recommended packages is no longer zipped: text, HTML, latex and examples files are now built when needed.
Options --use-zip and --use-zip-help in R CMD INSTALL are no longer available and --auto-zip only zips data (or not).
The help defaults haves been changed: they now are to use HTML help, not install prebuilt HTML help pages and not install CHM helpo be HTML help rather than CHM help (which is currently unavailable). [Not yet for the MSI installer.]
Binary packages are currently installed with all the types of help they contain [but that may change before release].