C# Precisely, by Peter Sestoft and Henrik I. Hansen, is a concise overview of the C# language. It is clearly intended for programmers that are already somewhat familiar with the language, but want to fill in the details.
I picked it up not because I needed the overview – there was little that I didn’t already know – but because I had read great reviews on the presentation format of the book. The presentation is, in fact, pretty impressive. As you read the book, the left page contains all of the prose, which is information-dense yet quite readable, and the right page contains examples and their descriptions, numbered from the beginning of the book to the end for easy cross-referencing. In only 180 pages or so, this book manages to convey a lot of information very efficiently.
I would definitely recommend this book to anyone that wants to get familiar with the details of C#. Be sure to read the online errata, as some of the information on C# 2.0 is slightly outdated. Also, as mentioned in the preface, this book does not cover a few topics, the most important of which are destructors and finalization; be sure to find another source of information for the missing topics.