I don't think Marilyn was a great actress in the technical sense but her ability to project raw emotion and sensitivity was amazing. I just feel warmth when I watch her, the on-screen charisma and magnetism she possessed was something even the most skilled of actors couldn't master. The best directors of her time attested to it, even Charlie Chaplin referred to her as "the greatest female clown".
Unfortunately, it's never been en vogue to praise the ability of sex symbols noted for light comedy, even though it's often said that comedy is more challenging than drama.