Too many books on ancient religions have been written from a perspective of "methodological atheism" or the assumption of the "superiority" of Christianity. Hornung takes Egyptian religion seriously, declaring that the gods were "not invented but experienced", and Egypt without its religion would be "a dark, uninhabited shell that would not repay study".
His principal contribution is to dismiss the common idea that the Egyptians, like some Hindus, regarded all gods as manifestations of one supreme being. He makes a good case for the Egyptian conception of reality actually being the opposite of the Greek one. For the Greeks, ultimate reality must be a unity. For Egyptians, according to Hornung, reality is necessarily plural: only non-being is a unity. Similarly, the Egyptian gods lack the concreteness of the Greek ones — they are "formulas rather than forms" — and he compares Egyptian theology to particle physics!
This book does exactly what it says in its title — it is not an introduction, nor a complete survey — but what it does do would be hard to better. Baines, himself an Egyptologist, has done an excellent job of translation, and Cornell UP deserve praise for their generous pricing.