One of themes I've always been fond of in The Godfather is tradition vs. modernity. I always loved that scene in GFII where Michael seeks the advice of his mother, the "traditional" woman...cleaning, cooking, raising the family AND NOT ASKING ANY QUESTIONS. When Mama Coreleone finally tells Michael "You can never lose your family..." Michael seems to shake his head in disbelief. His mother is a woman of another age and can't possibly understand what he means by the question...Michael then concludes that "Times are changing." And indeed they are.

To relate this to Kay, she personifies the new, "modern" woman's role. She demands fully equal footing in the marriage. She wants to know what's going on. She has a career. Michael would have obviously been much better off with Apollonia (a woman much like his own mother), the traditional Sicilian girl who knows in her blood that you don't ask questions about the Mafioso. So of course this tension, of Kay being the only "modern" woman amidst a sea of tradition results in conflict...which can make a person seem unlikable.

However, I completely agree with notions of Kay's naivete in believing that Michael, a full-blooded Sicilian, could somehow turn his back on tradition. When Kay finally realizes she's powerless to change him in the hotel room scene after Pentangeli's renegging, she even mentions "the Sicilian thing thats been going on for 2000 years." But Michael was quite naive as well, thinking that Kay would quietly go along with his gangster lifestyle as Apollonia or another "traditional" type would have. As a WASPy, modern American, Kay was doomed from the start. This line of thinking really makes you appreciate their exchange in GFI, "You know how naive you sound?/Who's being naive now, Kay?"