What is it about Hamlet that makes it more than just a complicated revenge tragedy?

The revenge play was a popular genre during Shakespeare's
time, one that audiences found quite entertaining. Hamlet features
the many standard conventions of the revenge play, but in Shakespeare's hands it became
an enduring literary masterpiece. The difference between Hamlet and
the revenge plays of Shakespeare's time is found really in your question--the word
"tragedy." Revenge plays were not tragedies, but Hamlet certainly
is, the tragedy developing from one of the most complex characters in literature, the
young Prince of Denmark.

It has been said that Hamlet is,
in fact, the first introspective character in English literature. The power of the drama
develops not from complicated external plot events but from Hamlet's tortured
examination of his own character--his feelings, his vices, his genuine and perhaps
unrecognized motivations. As the basic revenge plot advances, Hamlet is drawn more
deeply into himself, often reacting with confusion, guilt, and even self-hatred at what
he discovers. Unlike other revenge play protagonists, Hamlet shrinks from what he feels
compelled to do; his search for moral certainty traps him in inaction and further
self-contempt. Because of his very nature, he becomes a psychological prisoner of
circumstances he did not create and cannot change. It is the complexity of Hamlet's
character and his tortured introspection that lead to his destruction and elevate
Shakespeare's drama into the realm of unforgettable tragedy.