Bonus points if the author first mentions a specific trait, physical build, or whatever else halfway through the novel and totally fucks up my mental image.
I don’t expect a biology model description for each character, but write me something brief and evocative of how they should look, you fucking dork author. I don’t even know how tall she should be, her hair colour, anything. Why are you like this, author?
I believe character descriptions became a big thing in the time of physiognomy – when Balzac narrates someone’s physical appearance, he wants you to extrapolate the character’s personality from that. Physiognomy fell out of fashion and if there is no other motivation to provide a description, like signalling someone’s class position or injecting a bit of lyricism, it’s simply economical to leave it out. To provide a counter-example, Mary Gaitskill always writes exactly one paragraph of description in her short stories which you can just skip because it’s not properly integrated into the story as a whole.