Why does Hamlet Delay? -- Why the question is asked in the first place: Comparison to The Spanish Tragedy, Titus Andronicus, Macbeth, and The Lion King. -- Actors (Stephan Segal, for instance, have made whole careers out of doing revenge stories. -- Hamlet is a revenge story which has melodrama (violence, deceit, and madness) without satisfaction.
Various solutions to the problem:
the view, popularized by Goethe (1749 - 1832), "that Hamlet, for temperamental reasons, was fundamentally incapable of decisive action of any kind." -- Coleridge (1772 -1834) described Hamlet as one in whom "we see a great, an almost enormous, intellectual activity, and a proportionate aversion to real action consequent upon it."
the view that the "extrinsic difficulties inherent in the task were so stupendous as to have deterred any one, however determined."
In 1903 Andrew Cecil Bradley (1851 - 1935) summarized: See the Q & A.
1910, Ernest Jones:"The Oedipus-Complex as An Explanation of Hamlet's Mystery: A Study in Motive."
-- 1921: T.S. Eliot's very famous (and very snotty) essay, "Hamlet and His Problems," in which Eliot defines "objective correlative" and declares that Hamlet "is most certainly an artistic failure." -- Laurence Olivier's Hamlet of 1948 -- Franco Zeffirelli's 1990 version starring Mel Gibson and Glenn Close -- I don't think it's an artistic failure, but T.S. Eliot points the way to something important: the play is not just a case study.
ALSO, Hamlet has more comedy that any of Shakespeare's tragedies. -- Compare to Othello and Macbeth
Ophelia about Hamlet's visit to her closet: "My lord, I do not know." This visit is something that Hamlet never mentions before or after. -- Compare to the elaborate business about the play within the play.