Reviews have come out - 84% on RT
https://www.rottentomatoes.com/m/the_post/
The average critic rating (7.9/10) is actually rather high. Just a hair under Lincoln (8.0), and higher than Bridge of Spies (7.7) and War Horse (7.0).
With The Post's recent win for Best Film from the National Board of Review, I think this could be one of Spielberg's best films in a long time. The RT score may not be the highest, but the ones who loved it really loved it.