"Anne Hathaway," like many sonnets, is about love and all those nice things that come along with it: sex, passion, and of course poetry. It's a message to the world from Shakespeare's wife that she and her husband were very much in love, despite the way other people might interpret his will. Their love is beautiful, romantic, sexy; sounds like a pretty good relationship to us.
"Anne Hathaway" convincingly argues that Anne Hathaway and Shakespeare were really in love.
"Anne Hathaway" shows that Anne really loved Shakespeare, but the only word we have from Shakespeare himself is his will. We can't be sure that he loved Anne the way that she loved him.