I listened to the version translated by Joseph M.F. Marique for the Catholic University Press of America and read for Catholic Culture.
Irenaeus, Tertullian, Clement of Alexandria, Origen, and Athanasius all read and quoted it, some quite authoritatively, while Athanasius called it 'that good book.'
But it's weird. And you start to feel sorry for the Shepherd. He sees 12 things of different shades a number of times, but when he doesn't understand every nuance his guide asks him every time if he's stupid. Well if he is, so am I.
There's lots of strange imagery here. But not as much crystal clear concrete teaching. And no mention of Jesus by name or title of Christ.
The teaching that a husband must receive back an adulterous wife if she repents seems at odds with some Old and New Testament passages.
If in fact it was written by the brother of Pope Pius I this presents another problem--lack of apostolic authorship.
These are all important reasons why it wasn't recognized as canon.
And some of the 'black men' and 'white men' imagery would likely be racially deconstructed in modern Western culture, though it seems to be symbolic rather than racial to me.