Final answer:
Yiyi is most likely evaluating Oscar Isaac on his ability to transform into his characters, rendering his performances authentic and adding specificity to his roles, which is a critical aspect of true storytelling.
Step-by-step explanation:
If Yiyi were critiquing Oscar Isaac and focusing on the actor's ability to transform for every role so profoundly that the audience feels like they're meeting a new person each time, then she is most likely responding to the evaluation question of character transformation and performance authenticity. Oscar Isaac's skill in becoming the character and making choices that define his performance highlights an essential aspect of acting which is often critically regarded as true storytelling. The specificity of his acting adds layers to his performances, making them memorable and distinctive, thereby eliciting such a positive response from a viewer like Yiyi.