I partly agree with this statement, but there are many other factors contributing to the appeal of the play, including the complexities of other characters apart from Hamlet himself.
Hamlet's own personality is a puzzle filled with contradictions. Hostile critics, such as T.S. Eliot, have cited this as a reason that the play is overrated—that it does not make dramatic sense because in Hamlet Shakespeare creates a character that is unrealistic, one whose actions lack clear motivation. In my view, Eliot totally missed the point of the play. Part of the reason Hamlet is so iconic is that it expresses the irrational, perplexing, unaccountable nature of the world and of people overall. Hamlet is the protagonist, but much of his behavior seems calculated to alienate the audience. He is apparently shamming insanity, but even so, his obnoxious and abusive actions towards Ophelia and others are difficult to excuse. Perhaps, however, the lines Shakespeare gives him to speak are so profound and persuasive that we reflexively respond to them and empathize with Hamlet's character and his situation. Like Macbeth, Hamlet represents the "dark side" but an agonized one where audience and reader suffer along with him. This, surely, is a major factor in the play's lasting appeal, which is almost unprecedented in literature. It also leads to a more general observation that we value Shakespeare as much for his being a great poet as we do for his ability as a playwright, or more precisely, that the extraordinary qualities of his poetic language are the key to his power as a dramatist.
The predicaments of the other characters in Hamlet, though not presented as forcefully as those of Hamlet himself, are similarly engrossing, even in the case of Claudius. Another of Shakespeare's strengths is his ability to present an "evil" character in a sympathetic light, as Claudius appears in the scene where he is praying. He knows he has done wrong and is honestly asking God for forgiveness. Here, he is pathetically just a man, in spite of being a power-hungry murderer. Even before this point, during the play-within-a-play scene, one almost feels sorrier for Claudius than for the others, though all are in some sense victims. That virtually all the major characters end up dead is perhaps emblematic of the overall victimization of humanity, which Shakespeare portrays even more effectively in Hamlet than elsewhere in his oeuvre, with the possible exception of King Lear.