Unfortunately The greatest piece of painting is not the Mona Lisa nor the greatest piece of film The Godfather.
Art is subjective and is also the most controversial argument ever made. It became so when a certain Austrian man got rejected from an Art School, not really. The beginning of its controversy begins with the question of what is considered art. But art is subjective and hence we don't know what is considered art so we are in a loop.
Art begins with nature. The earliest forms of art began with cave paintings. We began with a palm print on a wall, then we move to shapes, shapes then turns to objects of nature; man, animals, anything they can relate to. Though the first art forms discovered were shells and talons possibly made into jewelry. But then again art is subjective. Like nature art evolves to more. Evolution led to the use of tools, these tools then becomes object of art. While not particularly grandeur compared to now, they did with what they had.
As accursed as time passed by, civilization rose and fell. It matters not where nor when, they rise and eventually they fall but they also grew, every eventual fall of civilization would rise to a greater one, this means economical and cultural growth and thus resulting in subsequent growth of artwork. In the age of antiquity, we now have a sculpting, pieces of stones carved upon. And the evolution of metallurgy led to sculptures of iron, bronze and gold. Pieces of gilded artworks, jewelry, pottery, literatures; written on leathers, sketch on walls or engraved upon, great architecture lasting centuries and monument to last eternity.
The Mediterranean was the cardle for civilizations due to the ease of trade between empires and kingdoms thus some of the greatest civilizations in the age of antiquity lies there. And so lot of cultural influence be it minor or major happened, even when empires and civilizations fell, their culture lives on in some ways. The more famous of them is the cultural invasion of Greece to the Romans.
Art as a form also grows and changes throughout the ages, while the do experience change in styles and forms, the subject of art still stays mainly the same. Paintings and sculptures of people of powers; kings, leaders, deities etc, there are exists subjects of places, a landscape, a building perhaps, and sometimes simpler objects or events of significant importance. As time passes by through the ages even amongst all the changes, it somehow maintained a status quo, at least up until the end 19th century.
At the end of the 19th century came the movement of impressionism and post impressionism. This movement would be considered as the beginning to the start of controversies for most part. Before while paintings were mostly realistic though not to the point of realism, they were mostly in line with visual reality. A man is still a man with a head, four limbs and a body, you know it because you see it. In short, impressionism bend the pre existing standards and post impressionism broke it. Though not considered necessary a rule, they were a norms, art and culture when passed down throughout history up until then were traditional, hence taken as a standard. Though it was considered it abnormal in way and not necessarily accepted for some, they are now considered some of the greatest artwork in history. The names of Monet, Cézanne, Renoir and van Gogh have known to everyone and their works revered by all.
Then came the 20th century and came many more movements, ones more ridiculous then others in the names of traditional art. Cubism became a thing, or in a shorter definition; you don't have to be a artist to become an artist. Objective realism did not matter anymore in cubism. Another movement was Expressionism which similarly forgoes objective realism. And finally came Abstract Art, the créme de la créme of hate.
While cubism and expressionism still have subjects of reality; a human figure, buildings or anything even though they they have no semblance of realism, abstract art does not contain any subject and thus making it hard to judge. One can paint everything, to something to nothing. Abstract art can varies from a canvas painted with a single color to all color or sometimes even just an empty canvas. But if reality is devoid in abstract art then how we judge it.
Abstract art follows closely with expressionism in the form of abstract expressionism where realism matter not and subjects of emotions and feelings and taken into account. But we can't objectively judge emotions as they themselves are abstract. We can however judge other factors such as colours, palette, shades, textures, brush strokes anything which we can judge objectively. Right?
I once saw a clown running and jumping along a wall of canvas with a brush in hand against the canvas. He repeated the process multiple times form his so called art and unsurprisingly his audience cheered and clapped for him. art installation named 'Helena & El Pascador' is a number of goldfish in blender, 10 to be exact so that visitors have the choice to kill them. Unsurprisingly some of them were killed.
Not to say that all of modern arts specifically abstract art are bad. Jackson Pollock's paintings are some of the most vivid and vibrant paintings even if I personally find his technique dumb and I couldn't care less for his meanings. Another artist Barnett Newman whose paintings constituents of sometimes only two of three colours only. Even though his paintings contains only three colours at the most his colours are comprehensive to say the least. His canvas filled with every shade of a single colour, a red isn't just a red for Newman nor a purple or grey or violet or blue. And there is also Pablo Picasso whose works I don't find nothing of interest but everyone seems to like.
The simpler truth is that most classical paintings are old, centuries of time had passed from their creation and thus are considered antique and it is hard for modern artist to stand out when great artist had already made their mark. So there is somehow a need to be more, to stand out more so art now us forced to become different and for the most part form now has become irrelevant. This led to a multitude of works in name of art. After all, if I can paint a back dot on a white canvas and name it art as it depicts racism and white supremacy (obviously) and then I can call anybody who disagree inept and that they cannot appreciate art.
As a layman, most modern abstract arts are dumb. Whatever you are trying to depict is irrelevant in the eyes of majority. Even the most popular and expensive paintings are irrelevant in the eyes of many. What's pleasing in the eye for one does not mean it please the eye of all.