Wide Sargasso Sea

Wide Sargasso Sea - Jean Rhys I heard so many things about this book, yet i fail to see what is the fuss about. I cannot make sense of it. True, it relates the story of Bertha- Antoinette. A creole who went mad, just like her mother went mad. True, it meets some details that Jane Eyre encloses, and that one star i give this book is due to the original idea of rewriting Bertha's story. Yet, to what extend does this story relate Bertha's suffering? I do NOT sympathise with her. All I see is a fragmanted past, one which asserts Bertha's insanity and savageness? maybe. Unfortunately (imo anyway) Rhys attempt to give us a voice for Bertha FAILS.

Why does Rhys gives a whole part to Rochester? He is more present in the novel than Bertha.
Why does Rhys use the same voice for Rochester AND Bertha? It does not make sense to me.