The theme became clear very quickly; in fact, I had that portion of the puzzle solved without answering most of the actual clues. The only part I had difficulty with was the end, namely, the "NO2". I had figured out the H2O, but second guessed myself because I didn't like REDNO2 as an answer (I wanted "red dye no. 2", and considered entering those extra letters as rebus squares, only that made no sense).
The family and I saw the painting in question in person last year at a recreation of the famous ARMORYSHOW at the New York Historical Society in NYC. It was truly the most remarkable piece of art there, arresting and astonishing, even now, a hundred years after the fact. I also recall really liking Edvard Munch's art.
The peculiar aspect of the puzzle is the two separate mini-puzzles in the NE and SW. These were so much more difficult because of the relative lack of theme material and the large chunky areas of white space. I liked LATIN and AMEN next to each other, with the "prayers" pair of clues. How about ENAMORED and ESTEEMED together? I also enjoyed the reference to AIRPLANE, although "The Sequel" hardly lived up to the original.
It's an odd bird of a puzzle, but I enjoyed it.