If a vote were to be held by people with reasonable taste in literature, Hamlet would probably be chosen as the greatest work ever written. I am not sure that I would go quite that far, but I strongly feel that it is Shakespeare's greatest play and one of the greatest books ever written.
Hamlet is one of the few works that I turn to over and over again. A few days ago, I saw Hamlet for kids. It used the text of the play, but was radically cut down to ninety minutes and so had to concentrate on the plot and a few of the more famous passages. Even in this radically truncated form, the plays sheer genius shines through.
It almost certainly has effected the English language more than any other work with the exception of the Bible. Line after line of it has passed into common usage. The plot,filled with death, is unusual for Shakespeare in being an original creation. Most of all is the genius of the psychological exploration. All of the main characters are brilliant psychological explorations, but of course it is Hamlet who gets more than half of the lines in the play who is the great creation and the best single character in literature.
Hamlet is a character with which I strongly identify. I have far too much of him in myself. The genius with which his character is explored and the richness of that exploration beggars the imagination. Hamlet is a work where there is so much going on that one can never hope to absorb anything but a tiny fraction of it in a single reading or viewing. As such, you can return to Hamlet again and again and it always feels like a revolutionary experience.
Hamlet simply deserves its reputation.