Writing Billie off as just another dumb blonde does a disservice to Holliday. Billie's actually more clever than she thinks or her man lets her to think, and it troubles him when her true intelligence starts to show and she realizes her real worth. Although Holliday's Oscar win over the rest of the lovely ladies is baffling, her sensitivity and excellent comedic timing make the otherwise straightforward movie.
While it starts out fairly routine, with a bookworm VS blonde Pygmalion angle and some halfhearted American jingoism, the film very quickly becomes something special once Judy Holliday is given the narrative. This is her picture, she knows it, and she owns it. It's a beautiful performance - her pathos and her sensuality are all-encompassing.
Though a bit too didactic, something that plagues almost anything even-remotely feminist, this was still an engagingly well-crafted piece of storytelling by the underrated Cukor, who is the single best classic Hollywood director when it comes to working with female actresses and characters. I agree that Judy Holliday shouldn't have won the Oscar but she's wonderful in the scene in which she's playing cards.
If the oscar was for "Most Annoying Performance", then I agree, Holiday wins hands down...that voice was like nails on a chalkboard! But since the award was for acting, I don't see how Ms. Swanson could have lost that year. Her character in Sunset Blvd. has become an icon and that performance has stood the test of time, while Holiday's portrayal of a dumb blonde was mediocre at best.