There is much more story in this book than the number of pages really allows and it has the feel of an unfinished work (which it was).
By no means a bad book, I think one could compare it to say
the silmarillion vs the lord of the rings (different genres, but stick with me).
The Borgias were a lifelong interest perhaps even obsession for Mario Puzo and the intrigue, family politics and abuse of power are themes that he would explore more fully in the Godfather.
As such the Family has a great deal of source material in it, not all of which is fully fleshed out.
It is none the less an intersting read, but it lacks the vital spark that the author might have brought to it had he lived to complete it himself.
In fact so much was going on at this time that it occasionally swamps the characters and that's a pity because in flashes they are portrayed very convincingly. At other times, their deeds and actions become almost a litany and certainly much more like an outline than a finished work (hence the comparison with the simarillion).
For those who are interested, the story is set in the period 1492- 1520 or thereabouts and revolves around the actions of the Borgia Pope (Alexander) and his sons and daughter (Lucrezia).
The church of Rome was (it seems) utterly corrupt at this time and its leaders involved in the pursuit of earthly power and pleasure. This leads to wars, murders, torture and all manner of ill-deeds.
Overall well worth a read, particularly if you are interested in the history of the period.