Literary critics and Shakespeare experts almost uniformly hold the opinion that The Tempest is Shakespeare's "farewell play." This opinion is based upon three major points. The first major reason is that this was the last play that Shakespeare wrote completely himself, though he is said to have collaborated with John Fletcher on The Two Noble Kinsman (an adaptation of Chaucer's "The Knight's Tale") c. 1621.
The second major reason is the thematic similarities between Prospero as a magician and Shakespeare as a playwright. Briefly, Prospero stage directs the tempest that moves the plot of his own personally contrived drama and then commands the entrances and exists of each of the individuals whose lives he is manipulating. He does this with the help of his own personal stage manager, Ariel. Thus Prospero's abilities and actions in this encounter between the opposing factions of the play are akin to and dramatizations of Shakespeare's role as a playwright who does precisely the same things but on paper.
The third is posited by Shakespearean director Trevor Nunn. He points to evidence in the play's original program that indicates fifty-year-old Shakespeare played fifty-year-old Propsero. "William Shakespeare" is at the top of the list of players and "Prospero" is at the top of the list of Characters. Shakespeare may have in Nunn's words, said farewell to acting and to writing at the same time by acting the role of Prospero himself.