Catholic guilt. That's a term thrown around in my family a lot, and it's something that I identify with. If you don't have an Irish Catholic background, I can understand how you may become bored with the religious sermons and the shameful, guilt-ridden nature of Stephen's musings.
This book revolves around Stephen's relationship with Catholicism, his downward descent into sin, his upward rise and devotion, and then lastly his skepticism. His evolution is the story of the book. Beyond that, there is not much "happening" as some others may have pointed out. Focus on the character development and you will be rewarded.
I think I liked Dubliners better, but Portrait isn't far below the mark either.