We remember reading Ulysses in a course in college, and about halfway through the book (after the "Nausicaa" episode), kids began to get extremely frustrated with it. One kid in particular had been commenting on how beautiful the prose of "Nausicaa" is, and the professor, with a sly smile, pointed out that Joyce is actually parodying sentimental romantic literature for young girls (see Gifford's annotations on "Nausicaa" for more on this). The kid continued to say that that Joyce never shows his cards, that there's something to be said for laying it all on the table. Joyce appears in one stylistic guise after another, but he never (so the angry kid contended) wrote honestly and from the heart.
The frustration at feeling duped is a pretty normal feeling when you read Ulysses. It is a book that, on many levels, makes you feel dumb. But the more time you spend with it, the more you can get into Joyce's spirit of play. It's like being let in on an extremely sophisticated inside joke, and as you let up on your desire to understand the book, you start to get a kick out of his wordplay and his constant mocking of other literary forms.
And the whole point isn't just to mock – it's to make you realize what assumptions you bring to a book. Presumably, a lot of people read books to learn something, to try to find something that is instructive about their way of life. Often, a few months after you've read a novel, you'll forget most of it except for a few key moments or lines and a general sensation – the "thrust" of the book. What Joyce is doing with all of the parodying is that he's intentionally toying with this desire to get the general thrust of the book. He's throwing down one gauntlet after another, and by doing so he's making you realize that what we tend to pull from a book is often determined by our own desires and preconceptions: we get from it what we want to get from it. By inviting us into a spirit of play, he's forcing us to think harder about the book, to constantly re-evaluate it and to question our own role in relation to what the book means.
When Ulysses came out, most people didn't get it (not that most people do now). A big point of confusion was that people thought the whole thing was a satire and that Joyce was making fun of ordinary people like Bloom by comparing them to Greek heroes. But that's one point Joyce is absolutely sincere on. He's trying to elevate everyday people to the level of epic heroes – to make us realize how our pedestrian little lives are a part of the literary world, and to make us realize that they are worthy of admiration and literary attention. Despite all his parodying, Joyce writes with incredible compassion for his characters. One place we feel it in particular is in "Ithaca," when Joyce suddenly produces an extensive list of every last item in Bloom's cabinet. The compassion is there in the details, and you have to take a second and think: Look how much he cares.