For the most part, a very easy read. Even for a Very Short Introduction, the coverage is extremely abbreviated. Kerr touches on only a few of the topics covered in the Summa Theologica and just barely mentions anything else Thomas wrote (most commonly the Summa contra Gentiles).

The first three-quarters or so, at least, give a little feeling for the kind of theology Thomas espoused, and how he came to such opinions. This is useful.

The last bit purports to describe what happened to Thomism since, but it's way too brief to do that subject any justice. Further, since the span covered and the number of people who have responded to Thomas are so large, Kerr often mentions the name of some such opponent (or proponent), gives a vague description of what they had to say, and moves on after a few sentences. It's impossible to remember (or, frankly, even to grasp) who any of these people were and what they were about, with such a whirlwind tour.

The problem is that the scope of the book is far too great for its length. We'd really need several Very Short Introductions to do it justice, even minimally: one for the Summa, another for the Summa contra Gentiles, one for the later history of Thomism, and perhaps another for Thomas himself, discussing how he came by his opinions, as the first part of this book does.

It's the nature of the series that everything is treated briefly, but it's not an excuse for picking a subject that isn't amenable to this kind of treatment. The book is worth a quick read, but it's unlikely to satisfy anyone with any particular interest in Thomas.