This story is about the emergence of identity. Stephen Dedalus's consciousness is front and centre in the book as Joyce weaves together important vignettes from his life that all contribute to his hero's artistic realization. Language, as always, is vital to Joyce's understanding of how humans develop.
For instance, the first segment of the book begins with a fantastic childhood story that showcases Stephen's diction and syntactical choices--without his awareness of this fact. I enjoyed the subtle things about this part. For instance: Stephen sees his father's glasses only as "glass that his father looked at him from behind." Also, Joyce starts out the book's tacit use of Dante by rendering the regional pronunciation of "Auntie" as "Dante." That's how Stephen hears it, and that's how we do too. Another great moment is when Stephen is at boarding school and hears the gas vents "singing." He's unaware of his artistic potential, but Joyce is pointing us in that direction already.
But Joyce is not here to help us read. Rather, he wants to show us the ins-and-outs of a young boy's mind. That's a difficulty I can't blame anyone for having with his writing in general. It's something you either have to accept, deny, or shred, and then you can decide whether to read him or not. However, even if you go through those steps, you're already doing something that Joyce wanted in the first place. He's tricky that way.
In my honest opinion, a lot of people will love or hate this book. It's got dark colours throughout, gets murky when Stephen feels bad, but shines when he's on the verge of realizing himself. Joyce is destabilizing form to parallel the ups and downs of a young man's social, intellectual, and religious maturation. It's poetic that he chooses to write in this way, and particularly so for a young man. My advice is to read "Portrait" for a window into an early revelation in 20th Century English literature. If you 're happy with that, see what Virginia Woolf does with this style, and you won't be disappointed in the slightest.