The PR people are selling it as Britain's Sistine Chapel- which both undersells and oversells it. On the one hand the Hall is a more distinguished piece of architecture than the Chapel- which is just a glorified shoebox- but on the other hand when it came to painting the walls and ceiling Michelangelo was no longer available.
The architects were Wren and Hawksmoor who are acknowledged as great masters- and the painter was James Thornhill who was popular with the 18th century establishment because he was a protestant Englishman. He doesn't figure prominently in the history of art, but show me another British painter who could have carried off such a huge decorative scheme with anything like the same panache. It happens that he was Hogarth's father in law- and teacher. Hogarth was the more original artist but you wouldn't have asked him to do you a mural with lots of glorified royals and bouncing cherubs. His attempts to perform in the big bow-wow manner at which Thornhill excelled are feeble.
The Sistine Chapel is the Pope's private chapel. The Painted Hall is the dining room of a retirement home for sailors....
Here are some examples of Thornhill's work. I love how confident it is. Individual passages have real charm. He was also a fine colourist. The second image shows allegorical personages making offerings to the children of George I.