Detachment
The concept of openness is invoked by the title, and that's an apt description for Julius. He is open to experiences because he is detached from the American Dream surrounding him. He sees the City through his own perspective, making value judgments about things from his bi-racial, bi-ethnic background. Not only is he detached from his cultures of origin, he is also detached romantically, and he tries to reconnect with his matriarchal grandmother, a sign of reconnection no doubt, but he even fails that.
Investigation and curiosity
But is Julius unhappy? He certainly experiences unhappy moments, and he suffers ennui and disappointment, perhaps even regret. But mostly, Julius concerns himself with what can be gleaned from daily life. He enjoys taking walks, because it gives him a chance to use his imagination to amuse himself, as he interprets the reality around him, adding layers and associations until his thoughts converge on something. He is scientific and curious.
Life and meaning
Ultimately, the novel shows a quest for meaning, but the prose and the form help the reader to understand what the novel's argument might be, if there is one. Perhaps Open City is a suggestion that the City is a platform for experience, that it is an open mechanism that one can participate with in many ways, or few ways. It is diverse and overwhelming and impossible. Plus, he sees it from two separate cultural points of view, and the novel suggests that it is in that "point of view" that the meaning lies, because although Julius can't see the meaning, the reader can see meaning in Julius's character.
