Explain me the characteristics of the Monalisa that make it a masterpiece

Context: Considered an archetypal masterpiece of the Italian Renaissance, it has been described as "the best known, the most visited, the most written about, the most sung about, the most parodied work of art in the world". The painting's novel qualities include the subject's enigmatic expression, monumentality of the composition, the subtle modelling of forms, and the atmospheric illusionism.

The painting has been definitively identified to depict Italian noblewoman Lisa del Giocondo. It is painted in oil on a white Lombardy poplar panel. Leonardo never gave the painting to the Giocondo family, and it is believed he later left it in his will to his favored apprentice Salaì. It was believed to have been painted between 1503 and 1506; however, Leonardo may have continued working on it as late as 1517. It was acquired by King Francis I of France and is now the property of the French Republic. It has been on permanent display at the Louvre in Paris since 1797.

The painting's global fame and popularity stem from its 1911 theft by Vincenzo Peruggia, who attributed his actions to Italian patriotism—a belief it should belong to Italy. The theft and subsequent recovery in 1914 generated unprecedented publicity for an art theft, and led to the publication of many cultural depictions such as the 1915 opera Mona Lisa, two early 1930s films and the song Mona Lisa recorded by Nat King Cole—one of the most successful songs of the 1950s.

The Mona Lisa is one of the most valuable paintings in the world. It holds the Guinness World Record for the highest-known painting insurance valuation in history at US$100 million in 1962 equivalent to $1 billion as of 2023.

Answer: The enigmatic expression of the subject, the monumentality of the composition, the subtle modelling of forms, and the atmospheric illusionism made the Mona Lisa one of the most valuable paintings in the world.