William H. Leary, the senior director of records and access management at the National Security Council, summarized the EO on the White House Blog. Three points jumped out for me:
[The Executive Order] establishes a National Declassification Center at the National Archives to enable agency reviewers to perform collaborative declassification in accordance with priorities developed by the Archivist with input from the general public.
It eliminates an Intelligence Community veto of certain decisions by the Interagency Security Classification Appeals Panel that was introduced in the Bush order.
The Order also significantly modifies the “third agency rule” [TSB note: this is the previously sacrosanct government policy that information from another agency should only be released with that agency's permission] to permit re-dissemination of classified documents by receiving agencies without the approval of the originating agency, except when the originating agency has indicated on the documents that such prior approval is required.
It all sounds very good for the producers and consumers of historical documentation.