The story has seen mostly through the eyes of the lawyer, Utterson, and we do not learn the dual nature of Jekyll-Hyde until the last chapter. Would the story have been more or less effective if it was done, like the last chapter, as a first person narrat

In my opinion, it would have been difficult for Jekyll to be implemented as the "first person" narrator because of his involvement in the story. Utterson's narrative is reliable in that he shares what he knows..... Jekyll would have made an unreliable narrator.