While he's a major antagonist, Snow's motivations are largely driven by power, control, and maintaining the status quo. He doesn't really change or evolve throughout the story, and his character is primarily defined by his ruthlessness and cunning. He lacks the emotional complexity and internal conflict that other characters like Katniss, Peeta, or even Haymitch exhibit.
Here's why other characters aren't as definitively flat:
* Haymitch is a complex character with his own tragic past and struggles with addiction, even if he's often portrayed as cynical and grumpy.
* Peeta struggles with his own morality and the pressure of the Games, adding layers to his character beyond just being the "nice guy."
* Katniss is a multifaceted protagonist who faces moral dilemmas, develops her own agency, and experiences emotional growth throughout the story.
Ultimately, whether President Snow is the only flat character in *Catching Fire* is subjective. However, his lack of depth and one-dimensional motivation make him a strong contender for the title.