Well, the book is not just 2013 case law. Which is great news, because it makes the book a handy resource for nailing down the basics (like the prima facie elements of assorted employment law claims, for example). As a desk manual for the basics, the book does a great job.
Sure, you're familiar with retaliation claims. But are you familiar with the Supreme Court's decision in 2011 recognizing third-party retaliation? Maybe you are familiar with that case (Thompson v. N. Am. Stainless) . . . but have you seen the analysis of such claims from the District of D.C. and the Northern District of Florida (now you're just lying!).
That's the really great thing about this book. It takes the basics, and then tacks on new developments. It not only touches on new developments, but provides detail with summaries of district and circuit court decisions from the past few years. It's a great way to get caught up in areas that you may have heard of (like third party retaliation) but probably haven't actually litigated or kept up with the subsequent cases applying the new precedent.
Weighing in at 1290 pages of actual content (excluding index, table of cases, etc.), PLI's Employment Law Yearbook covers a broad range of topics from wage and hour to OFCCP to privacy law to guarding trade secrets to the ADA to . . . well, you get the idea. It covers a lot. Overall, the book is a great resource for the basics and cutting edge employment law developments alike.
Disclaimer: I did not receive any compensation aside from a copy of the book with a simple request to review it and provide my thoughts.