This is an account of the Norsemen in the period A.D. 800-1200, and is written primarily for the general reader but will also serve the needs of many university students.
I will not comment on this book's value as a secondary source because I'm not an expert, and I've only just begun studying this subject formally. I also want to make it clear what exactly this book is: a dense, scholarly tome, stuffed full with information but a little dry to read. In short, I would not recommend it as a book for people with only a passing interest in viking culture. The language is often archaic and convoluted, and it is in no way an easy read. I, personally, loved reading it, but then I love the subject.
However, if you are interested in diving into the world of Viking scholarship, The Viking Achievement is a good place to start. It doesn't give a narration of important events or figures, but instead provides a background for everything. It contains detailed and learned analyses of various aspects of viking culture, from gender roles and slaves to poetry and art. For a lot of people the history is the fun part, but having a sense of the culture behind all past events really is essential for really understanding it. Essentially, I would recommend this book to anyone who seriously wants to study and understand the viking world.
Just a short word of warning: This is an old book, and parts of it are outdated. It does not include modern findings and interpretations (as Foote acknowledges). There are also multiple references to archaeological sites that had not been fully excavated at the time of writing, but have been now. I'd say it's worth looking them up when he mentions them. Essentially, it's a good text for establishing what kind of society we are talking about - something that many people do not consider.