In the context of a film that by design has a thin plot and characterizations, Monroe's performance is interesting.
She makes fun of her over-enunciation, which acting coach Natasha Lytess forced on her in River of No Return; her desire to act in serious roles (her character mentions The Cherry Orchard); her driving ambition to be a star; her fights to shape her career, down to the clothes she wore; and even an allusion to having affairs with powerful men.
Then there's the strange irony that she was forced into the role and disliked by the other actors, just as her character intrudes on their lives and is disliked by Merman's character.
Aside from that, it's interesting to hear her natural voice. She doesn't play a dumb or innocent bunny. She plays a mature woman of talent who has a career goal. Her acting is less hokey than the other actors' performances. All three of her songs are well done, including the charming Lazy.