The Cambridge Companion to Classical Islamic Theology is a good introduction to the topic of Islamic theology and its relationship with Sufism. It was edited by Timothy Winter, known to Muslims as Shaykh Abd al-Hakim Murad. The essays are by many well-known and highly respected scholars, such as Shaykh Umar Faruq Abd-Allah and Yahya Michot.
The essays are mostly introductions to their topics and do not delve too deeply into the details. In fact many of them end right when things seemed to start to get interesting to me, for example Steffen A. J. Stelzer’s highly interesting chapter on ethics.
The book could have as well been titled An Introduction to Islamic Theology. This makes it different from other Cambridge Companions I have read where scholars delve deeply and present new interpretations and theories of their own. Here the scholars almost entirely limit themselves to presenting overviews of the topics they discuss, which is beneficial for beginners to the topic, but not so beneficial for those wishing for detailed discussions.
The two exceptions are Steffen A. J. Stelzer’s essay on ethics and Toby Mayer’s essay on theology and Sufism, which present new and interesting analysis.