Reddit reviews God's Caliph (University of Cambridge Oriental Publications)

In terms of academic works, a few more to take a look at would be The Charismatic Community: Shi'ite Identity in Early Islam by Maria Massi Dakake, God's Caliph: Religious Authority in the First Centuries of Islam by Patricia Crone and Martin Hinds, The Succession to Muhammad: A Study of the Early Caliphate by Wilferd Madelung, and The Origins of the Shī'a: Identity, Ritual, and Sacred Space in Eighth-Century Kūfa by Najam Haider. None of these I would give my 100% approval too, but they are interesting historical takes on the topic in a more critical fashion than you'll often find.