This is a book basically covering Church history from Pentecost (circa AD 33) to Constantine making Christianity legal in AD 313.
McKechnie is generally coming from a background that I agree with - he says the New Testament is a good source for early church history, though he argues his case well rather than just assuming it.
McKechnie pays particular attention to the dating of the New Testament, the relationship between the Church and various heretical sects and other groups, as well as the role of women in the early church (which was jolly interesting). Where there's a debate on something, of course, he outlines the main positions and states and explains his own view, which I usually found persuasive.
I guess the area I'd most like to see strengthened in this book is the theology. Not that it's dodgy - just that there's not much of it and I'd have been interested in some of the theological discussions and relationships between groups, etc.
As fairly basic (250-odd pages) introductions go, it seems informative and very good. There are certainly issues I'd like to know more about, but at least I now know what the issues are and have a better general picture.