I always think of the building (and brutalist architecture in general) as absurdist architecture, and I find City Hall to be quite humorous in that light.
The general shape lifts up and is trying to appear as if it's floating, in contrast to the material selection. Think of an Elephant ballerina, or Douglas Adams "It hung in the air in exactly the way bricks don't".
Another example is the Holman government building a few blocks away - with these ridiculous stairways through a massive open space underneath an imposing bridge of offices.
Pure absurdist humor.