Now look at 333 W. Wacker, which oversees the bend of the Chicago River. The modernist way to build something here would be to clear a lot and put up the biggest box space would allow. But the architects opted for "contextual architecture," designing a building that is sensitive to and interactive with its natural context. Not only does its curved profile emulate and enhance the natural bend of the river, but its face of greenish glass mirrors the color of the water. The result is a stunning design that gives its natural surroundings an aesthetic resonance. The building also serves as an attractive "back door" to the city as you approach from the west--an alternative face to the familiar "front door" view of Chicago that tourists enjoy from Navy Pier and Michigan Avenue.-NB

Blair Kamin:
Consider the different contexts addressed so handsomely by the twin faces of 333 W. Wacker Drive, the 1983 office building by New York City architects Kohn Pedersen Fox. A graceful arc of green glass makes a sculptural statement that works in the wide-open context of the Wacker Drive river corridor; meanwhile, the building's other facade, which is sliced and notched, suits the grittier, more confined district of the Loop. Not only that, the color of the glassy, 36-story tower blends beautifully with its classically influenced stone base."
-from the Chicago Tribune

From the building's official site:
This landmark building creates a dialogue between figural and abstract expression. In one sense, it can be viewed as a classical composition of three parts: base, middle and top. Simultaneously, it can be seen as an abstract composition, the architectural equivalent of a Brancusi sculpture.
-More from KPF.com including my favorite picture of the building (see this one too)