It's a short book basically about an old man spending days trying to catch a really big fish, while talking to himself about Joe DiMaggio and whatever else pops in his head. If that already sounds like too much of a snore-fest, this probably isn't the book for you.
But if you give it a chance, what a story! It puts other Man vs Nature stories to shame. Hemingway puts you in the boat with this old man, and watch his fortunes rise and fall, and how he copes with physical and mental pain, alone and far from shore.
For such a short book, by the satisfying end, you leave feeling like the the old man's constant friend, the boy: sympathetic for the old man's struggles, but in complete admiration of his spirit.