Ulysses is a snapshot of one day's life. Ulysses has been labeled dirty, blasphemous, and unreadable. It is funny, sorrowful, and even suspenseful. And despite the exegetical industry that has sprung up in the last 75 years, Ulysses is also a compulsively readable book. Even the verbal vaudeville of the final chapters can be navigated with relative ease, as long as you're willing to be buffeted, tickled, challenged, and (occasionally) vexed by Joyce's sheer command of the English language.
Among other things, a novel is simply a long story, and the first question about any story is: What happens?
In the case of Ulysses, the answer might be Everything.