The design language since the introduction of the unibodies has used curved tapers to make the laptops look thinner than they are.
The new design language ignores that completely, with everything squared off but radii used everywhere to blend the sharp corners. Small radii for the display module, and a larger radius for the underside of the body.
However, the difference in thickness between the older retina display models, and the new design is insignificant in real terms.
I really, really like the new design.
(But I also really like the way the display has been extended either side of the camera module, so take my taste in industrial design however you want!)