Why is Huckleberry Finn so important?

Can you explain why Huckleberry Finn is considered a seminal work in American literature? Is it due to its portrayal of racial tensions and the struggle for freedom during the antebellum period? Or is it because of its unique narrative style and use of vernacular dialect? Additionally, how does the novel's depiction of the Mississippi River and its inhabitants contribute to its significance? Finally, how has Huckleberry Finn influenced subsequent generations of writers and readers?