Chell in Portal 1 is dirty and uncleanly; there's a sense of disorientation in her that gives credulity to Portal's narrative. She really looks like someone who is moving through perpetual white rooms, falling hundreds of feet at a time, only held in place by cold, steel mechanisms bolted to her bare leg. A loud, omnipresent voice fills the room, telling her where to go, what to do, with a subtle, frightening subtext of consciousness. She's also alone, to her own thoughts, for a very long time.
In comparison, Chell in Portal 2 looks like she's going to the gym. She looks clean, younger and healthy. Her lips are glossy and opaque, as opposed to dry and unkempt like before, where you can even see some dead skin. Her hair is in this neat tie thing, that falls to the sides of her face in this way that feels constructed, like she thought of that, like she had the time and energy to carefully construct her appearance, which she absolutely does not in Portal 2's setting.
It's sort of a good example of a very subtle, casual kind of male gaze. I hesitate to call it problematic, as she does look like a normal human being, but it's definitely dissonant with its narrative. And I feel like it perpetuates an idea that women, even in the most straining, horrible circumstances, can and probably should be able to keep up that level of appearance. So I guess it is pretty problematic. :/
I'll leave you to your thoughts.