For being such a slim novel, James Joyce's A Portrait of the Artist as a Young Man is open to a wide variety of interpretations. I think it's helpful to approach it from a broad perspective to start with, and so I'll answer this question by considering how we're...
For being such a slim novel, James Joyce's A Portrait of the Artist as a Young Man is open to a wide variety of interpretations. I think it's helpful to approach it from a broad perspective to start with, and so I'll answer this question by considering how we're meant to interpret Stephen as an artist by the end of book, since Stephen's maturation as an artist is the focus of the story. In my view, Joyce wrote the novel not to present Stephen as an exemplary artist (as most people assume), but rather to give us a portrait of an overly ambitious youth who arrogantly assumes his artistic ability is greater than it is.
This opinion might be surprising for many readers, as the book is about the growth of an artist. As such, the natural assumption would be that Joyce is showing us a radically talented young man who will "forge in the smithy of my soul the uncreated conscience of my race" (253). Furthermore, if we look at the novel as an isolated entity, it seems as if Stephen is pretty successful: the book ends with him leaving home to pursue his art abroad, after all.
However, once one reads Ulysses, it becomes increasingly difficult to see Stephen as a great artist. The novel starts with a disenchanted and penniless Stephen living back in Dublin. It becomes apparent that his attempts to become a great artist have failed, and so he's resigned himself to teach at a school in Dublin. Deeply in debt, Stephen is also beginning to develop something of an alcohol problem. With this fate in mind, it becomes increasingly difficult to read Portrait in a positive light. After reading Ulysses, Stephen's character in Portrait seems hopelessly arrogant, less of a genius artist and more of a self-important blowhard who's overly interesting in talking about himself and his supposedly great abilities. Within this context, Portrait becomes Joyce's critique of the idealism of youth, as he shows it to be misguided and out of touch with the harsh realities of the world.