Well that only took me a year...
Of course, it's a must read for every Lutheran. This is crucial to have on your shelf if you want to understand what Lutherans teach and confess. But if you read any one item from this, read the Formula of Concord at the back (Solid Declaration and Epitome). It's shorter than the Augsburg Confession and the Apology, and I think it's a clearer with better vocabulary. That was my favorite part.
The main pieces of the Concordance are:
The three creeds (Apostles' Nicene, Athanasian)
Luther's Small Catechism
Luther's Large Catechism
Augsbug Confession (written by Melanchthon)
Apology to the Augsburg Confession (written by Melanchthon)
Smalcald Articles (written by Luther)
Treatise on the Power and Primacy of the Pope (written by Melanchthon)
Formula of Concord (containing the Solid Declaration, and its abridged version, the Epitome) (seems mostly written by Chemnitz)
These are the major parts, all set in chronological order. The creeds and catechisms are short, fast, useful summaries that are easy to get through. The Augsburg Confession and Apology are long and tedious, but still important. The Smalcald Articles and Primacy of the Pope are short, but seemingly random and not comprehensive. I think the Formula at the very end is the most well-written and the best summation of major points in Lutheran theology, as distinguished from other denominations (past and present). Luther's writing is fiery, Melanchthon's writing is boring, and Chemnitz's writing is pleasantly methodical.
This second edition (reader's edition) has fantastic resources dispersed throughout the major parts of the Concordance. This includes: Prefaces to the first and second editions, a general introduction, notes about this edition and translation, historical notes about when the documents were first written and distributed, notes about how to use the book for study purposes, a user's guide to the formatting, an overview with explanations of all the major parts, a year-long reader's guide that will help you read through all the major parts, a timeline explaining major dates of the reformation, an editor's introduction to each major part explaining the context for writing each piece, notes on understanding indulgences, and explanations of the context for controversies surrounding the writing of the Formula. The Appendixes include a catalogue of testimonies with excerpts from church fathers, an exhortation to confession from Luther's Large Catechism, and the Saxon Visitation Articles. At the back is a glossary of terms, a list of descriptions of people and groups who were major players in the Reformation, an index of Bible references noted throughout the Concordance, a subject index, and a map of Germany.
The wood carvings included throughout really add to the reading experience. Particularly with little explanations of VDMA and Luther's rose, depictions of the people writing, and in the Small Catechism sections where Luther goes through the 10 commandments and petitions of the Lord's Prayer. One item is placed on each page, with an accompanying image. In the back there's a bunch of color plates, showing important artwork of the time (including some of Cranach's most famous pieces). Along with these images are figure legends that paint a "visual overview of the Reformation."