The more that you know about the setting of Ulysses, the more sense it makes; yet with very little context you can get a great deal from it. Early on, a character remarks that Shakespeare is the happy hunting ground of minds that have lost their balance; if Joyce aspired to supplant Shakespeare there, he did pretty well, which is to say that there is a thriving Joyce industry. I haven't read much of its production, but I recall Hugh Kenner's Joyce's Voices as pretty good. If you haven't already done so, read Portrait of the Artist as a Young Man and Dubliners, for many characters from both crop up in Ulysses.