“This is not supposed to look like a sexy Marvel superhero suit. It’s supposed to look like it was designed without any thought of making her look attractive," said Valve's concept artist, Matt Charlesworth. "We don't want to make her be unattractive, but we want to balance that out. Chell is a test subject, so she should look like one. Not a prisoner or a janitor or something."
"Everything should look 10 times better than the first Portal, that's the goal," Charlesworth said.
I'm glad they're sticking with Chell instead of introing a new character. The way Portal never focused on the main character's background or traits was affecting. Experiencing the game through the eyes of an anonymous test subject made "her" into "you," get what I'm saying?
Also, importantly, those awesome spring-jumping heel things are back, so you won't have to worry about death from falling in the new game. Check out the interview for more.
Source: Game Informer