The drama of the story is very clearly drawn, yet the outcome of the story is always in question. We know very clearly what is happening on a factual and an emotion level, but we don't know what will happen at any point in the book.
This idea points to an achievement of tension and suspense as well as a strength of "scenario".
The strength of the novella is in the simplicity. Man and fish. Man versus fish. Man and boy. Then there is another deeper level of complexity beneath that apparent simplicity.
Another strength of this novella is the unique relationship between Manolin and Santiago. Manolin learned how to fish, with a passion and love, from Santiago. Though he is now on a "lucky" boat, Manolin is not happy. "The old man had taught the boy to fish and the boy loved him." One of the things we connect with in movies or fiction or even real-life stories is the relationship between characters, and that's certainly true of The Old Man and the Sea.
One of the strengths of The Old Man and the Sea is the narratorial structure. A third person limited narrator tells the tale of Santiago's luck gone bad through the perspective and consciousness of Santiago himself. Santiago is a fisherman and has not caught anything for eighty-four days. Through Hemingway's narratorial technique, the the reader gains insights into how Santiago thinks and feels. For example, the narrator says, "[The old man's] hope and his confidence has never gone. But now they were freshening as when the breeze rises" and "He was too simple to wonder where he had attained humility. But he knew he had attained it and he knew it was not disgraceful ... ." Further, the reader also gains insights into Santiago's life as either the narrator discloses current events around him or the boy discloses his life by recounting past events. For example, the narrator says, "Others, of the older fishermen, looked at [Santiago] and were sad. But they did not show it ...," and the boy says, "I remember the tail slapping and banging and the thwart breaking ...I remember everything from when we first went together."