Besides the Burgess book mentioned above, you might look at the older standard reference Stuart Gilbert James Joyce's Ulysses: A study 1930. (It should be available in paperback.) Wikipedia also has a nice synopsis of the book (link). Joyce wrote the way he did because he enjoyed it, and because he thought he was on to something. Novels took a turn in the 19th century and started concentrating more on the psychology of the characters and less on plot. I'm thinking of authors like Dostoevsky, Huysman, Proust. We still see this distinction today between plot- and character-driven novels and films. I was in Dublin on 16 June 1982, when over 200 actors performed The Wandering Rocks episode from the book, simultaneously throughout the city. In the end, the appreciation of most art comes down to the personal taste of the consumer. If you don't like Joyce, skip him. If you want to read Joyce before he settled on stream of conscious, read The Dubliners.

On the subject of mental illness, Joyce's daughter Lucia was mentally ill.

Ceci n'est pas un seing.