This one is pretty pleasing to the eyes.
You can control the mapping of classes of rectangles to characters by editing #(4 4 1 3 0 2) and the characters themselves by editing "█▓▒░ ", to experiment with your own designs. The current classes of rectangles can be obtained by painting the rectangles with their class numbers:
44500544
13522531
13522531
44500544
4114
4334
5555
0220
0220
5555
4334
4114The class assigned to a rectangle within its grandparent is the index of the first predicate that holds in the preds list of predicates within the outer symbol lambda, with an implicit final predicate that always holds.