You and me, both.
Like all art, its "greatness" is subjective and comes from various sources, those keepers of avant-garde and trend-setters in the art world.
Personally, I like this Vermeer--also at the Lourve--much better:

I also like that painting (The Astronomer) much better. Not only is it more complex than Leonardo's opus, but it subtly shows the connection of science and God, portraying a book on astronomy that called on scientists to seek inspiration from God, and on the wall can be seen the Cornelius de Vos painting The Finding of Moses (c. 1635).