Dan O'Herlihy performance here is basically a one man show for a good amount of the picture. He portrays Crusoe quite well, because he stays interesting throughout his performance. He is able to stay interesting and is able to be easily followed through what he does to survive on the island. O'Herlihy importantly never becomes boring as Robinson Crusoe moves through his tasks to survive his ordeal. He importantly acts as perfect guide as he goes through the motions of survival.
Robinson Crusoe though is not a completely simple character who does not at all change through his ordeal. He indeed matures throughout his time alone. He moves from a man who is slightly lost almost in his survival but slowly grows to fully triumph in his ability to achieve survival alone. O'Herlihy shows the change well without over showing his changes. I think even more effective are when Robinson Crusoe examines his own life, and faith in key scenes that really show O'Herlihy skill well. His fever scene where he hallucinates of his father is incredibly effective due to O'Herlihy who manages to show a lot of the man Crusoe was before his predicament in this single scene. His scene of examining his faith, and facing it are again very well portrayed by O'Herlihy putting a lot of strength and power into these moments.
O'Herlihy always remains believable in his role, and adds the believability needed for the story, even in scenes that sort of stress this very hard such as his first encounter with Friday, or the scene where Friday puts on a dress, or in fact just about anything with Friday. Even in scenes like the ones with Friday being rather prominent O'Herlihy stays true to his character he has developed well, and since he stays steadfast in his portrayal he causes the film to be far more effective, and believable. I would never say O'Herlihy's performance is amazing but it always works well for the film, and completely serves its purpose.
