What is Coral-Gables, FL, like as a city to live in?

I might be spending next year there, studying at the University of Miami, and (as an english person) have no idea what kind of a place it is. Is it upper-class, middle-class or lower-class? How expensive is it? I read that it is 'a gated-community'; is this true? If so, what exactly does that mean? Thank you! :D