Despite being a somewhat flawed/schizophrenic fan of Joyce - obsessed with Ulysses and Dubliners and their air of perfection, bored with Portrait and mystified/annoyed by Finnegans Wake - I have always avoided reading Stephen Hero. It's generally seen as an alternative version of Portrait, and I think that was my sole reason for not reading it.
Stephen Hero is not only unfinished, it seems to be miles from the end, if we indeed think of it as a different version of Portrait. Joyce worked on this my-life-disguised-as-fiction book between 1903, it is thought, and 1905, when he abandoned it to make a start on Portrait.
Needless to say, many of the themes later refined to end up in both Portrait and Ulysses are present: the development of a thinker poised between literature and religion, piety and sin, and above all an examination of Stephen's relationships both intimate and formal in the world around him and in his own expanding inner world.
The younger Joyce was not noticeably less of a stylist than the man who wrote the later books, and Stephen Hero is, mostly, very elegantly written, knowing when to swerve detail for the bigger picture and when to linger over it. It is an engaging book, and as always with Joyce, not flawless, exactly, but with it imperfections only exposed because they stand out of a more complete would-be masterpiece of a book.
I'm now re-reading Portrait, and finding it, firstly, fascinating - my disdain for it a mystery - and secondly, lacking in some of the parts of Stephen Hero that didn't make it through to the later book.
As to whether I recommend it, as ever with Joyce: if you're into Joyce, don't be like me, and ignore a book as important as Stephen Hero. If you're not into the quirky manifestations of a very hard man to like, then... leave it, and read something else.