Mencius (yes, a one-word title, which is also the name of the principle author/subject), was a Confucian sage in the 3rd century BCE, about a century following Confucius. Apparently, other than this book bearing his name, little is historically known about him. This is a collection of his sayings by his students, so is as much about him as it is a collection of his sayings. The book itself, in the Penguin Classics edition, is a translation by the noted scholar D.C. Lau, which was originally published in 1970. This features extensive additional material by Lau, explaining much of the context of the work, and how it came down to us.
From what I've been able to gather from this, it appears that Mencius was a “mainstream” Confucian sage at a time (a century on from Confucius himself) where there were various other schools and traditions branching off. A number of these other schools come up repeatedly, as Mencius argues against them (and, other than their appearances here, I have no idea how well known these are within what survives from that period). Mencius seems to be known best for his use of analogy, and much of the book involves his interaction with various figures of the time.
I am only peripherally familiar with Confucian thought, so it's hard for me to make much direct commentary on how Mencius operates within that tradition, but much here is set within a framework or expected religious rituals, and requirements of the various levels of society, with a whole panoply of very specific particulars, which seem strange at best from a modern cultural perspective. To give you a taste of how much of the book unfolds, here's a section (Book II – Part A - #5) which at least played to my Libertarian sensibilities, a couple of dozen centuries after the fact:
Parts of this are fascinating for their details on how ancient Chinese society was structured … with various levels of officials, down to various levels of “Gentlemen”, having income from certain amounts of land, and how the land was distributed, taxed, and regulated. There is also quite a lot of “history” involved, but it is hard to track this, as the time-line in the Mencius book is not necessarily in agreement with other texts of the time (Lau goes into this in some detail), and in many cases there is only sketchy historical materials apart from these texts to go from.5. Mencius said, 'If you honour the good and wise and employ the able so that outstanding men are in high position, then Gentlemen throughout the Empire will be only too pleased to serve at your court. In the market-place, if goods are exempted when premises are taxed, and premises exempted when the ground is taxed, then the traders throughout the Empire will be only too pleased to store their goods in your market-place. If there is inspection but no duty at the border station, then the travellers throughout the Empire will be only too pleased to go by the way of your roads. If tillers help in the public fields but pay no tax on the land, them farmers throughout the Empire will be only too pleased to till the land in your realm. If you abolish the levy in lieu of corvée and the levy in lieu of the planting of the mulberry, then all the people of the Empire will be only too pleased to come and settle in your state. If you can truly execute these five measures, the people of your neighboring states will look up to you as to their father and mother; and since man came into this world no one has succeeded in inciting children against their parents. In this way, you will have no match in the Empire. He who has no match in the Empire is a Heaven-appointed officer, and it has never happened that such a man failed to become a true King.'
Again Mencius isn't exactly a “for everybody” book, but if you have an interest in ancient society, the history of China, philosophy in general, and Confucianism's development in particular, this may be of interest to you. As noted, the used copy I got is over 40 years old, but this edition is still available, with “good” used copies for as little as a penny. If this is “your thing”, and you've not read Mencius yet, you will likely find this quite rewarding, but it's hardly an “all and sundry” recommendation.