We're going to make a bold assertion here because we can't help it: the last several pages of Ulysses are some of the most breathtaking prose in the English language. In other words, if you can't truck through the other 780 pages, at least read these.
The last 50 pages of the book are written with no punctuation as the swirling thoughts of Molly Bloom. She is lying beside her husband Leopold in bed (they sleep head to foot) and thinking about her day and their life together. While most of the book has been focused on the minds of Leopold Bloom and Stephen Dedalus, this is the first major move to a female point of view. Leopold has thought extensively about Molly's affair with Boylan, and we glimpse some justification for it beforehand (namely, that Leopold has not made love to her for ten years, since the death of their son Rudy). Here, though, we are pushed through Molly's thoughts and feelings and come to see her in a sympathetic light.
Molly was modeled on Joyce's wife, Nora Barnacle, to whom he was married all his life and with whom he was passionately in love. Nora was from the west of Ireland, and in contrast to Joyce's historic erudition, she was a down to earth woman who didn't even think Joyce was much of a writer. As she famously put it, James should have stuck to music (source).
At one point, there was a rumor going around Dublin that Nora had slept with an acquaintance of Joyce's early on in their relationship and that it drove Joyce nearly mad with jealousy. More likely than not, it was nothing but a rumor, but for Joyce it became an incredible neurosis. For all of his genius, one thing Joyce couldn't imagine was having the person he loved most make love with someone else.
One way to think of the end of Ulysses is to understand it as Joyce's attempt to imagine his wife's point of view, to imagine how a woman could cheat on her husband and still love him. Whether or not he succeeds in blowing open a female perspective is a matter of critical debate, but this is an honest try. While many other points in the book parody other types of prose and can't be separated from ironic self-awareness, here Joyce elevates his writing as much as he is able.
The end of Molly's monologue focuses on the day that Bloom proposed to her at Howth's head. This might be seen as a sort of victory for Bloom. Despite the fact that Molly slept with Boylan earlier in the day, her last thoughts before she sleeps are for her husband. Bloom asks her to marry him and her mind rushes back to her youth and to former lovers and to a thousand things that a man may never imagine a woman thinking about before agreeing to his proposal. But then Molly asks Bloom to ask her again, and the novel ends on a resounding note of affirmation:
"…then I asked him with my eyes to ask again yes and then he asked me would I yes to say yes my mountain flower and first I put my arms around him yes and drew him down to me so he could feel my breasts all perfume yes and his heart was going like mad and yes I said yes I will Yes." (18.783)
This statement is a re-affirmation of Bloom and of life itself in spite of all the burdens we have seen throughout the novel: the death of a son, the suicide of a father, a sex-less marriage, the resignation of middle age, and life in a demoralized city held under the thumb of British rule. It is, you might say, happiness in view of all else.