The Lacedaemons were never the same after their defeat at the hands of the Thebans @ Leuctria in 371BC. A good chunk of this book (about 1/3, in fact) is spent on Agis & Cleomenes. These personages were post-Leuctria fellows who tried to resurrect the Lycurgan principles and traditions which the Spartans were so well known for. Both failed, but gave noble efforts to these ends. Basically, they represented the death-knell to the hardcore Laconian way of life.
Now, both figures are certainly important to classical history; that much is not in debate. However, confronting them in a book entitled "On Sparta" by a historian the calibre of Plutarch is a bit anti-climactic. Again, I was so looking forward to reading about this magnificent culture while it was in its prime - cover to cover.
On the upside, the best part of the book deals with Lycurgus. It was he who founded the famous "Spartan way of life" around the 8th century BC. It was he who contrived such innovations as the long hair on Spartan males, the Lacedamonian distaste for $$ and all things artistic (with the exception of music) as well as virtually all luxuries and comforts of life. It is because of Lycurgus that the Laconians who came after shunned all things effeminate and became such a brutal fighting force. It was also he who promoted egalitarian distribution of land - noted as his most significant reform. Here Plutarch furnishes one of the most detailed biographies of this great man that you will find. The chapter on Lycurgus alone is well worth the price of the book.
In the remainder of the treatise, Plutarch displays sundry quotations of Spartan kings, warriors and women [it is ironic that in such a militaristic state that Lacedaemon women had more rights and privileges than any other city state in Greece]. There are many salient quotes that exemplify Spartan ideals quite nicely.
If you're looking for a book on Sparta, you can do much worse than this one. I will continue my search for more books on Sparta during her heyday. In the meantime, I will have to settle for daydreams about Lycurgus.
I will leave you with one of my favorite Spartan sayings (this one by King Agesilaus):
"Courage has no value if justice is not in evidence too; but if everyone were to be just, then no one would need courage." (P. 119)