This is a book of political philosophy that has reached the level of a classic. John Locke sets out to explain how political society emerged, how the state has both legitimacy and limits to it, and how natural rights are a universal reality.
He begins by addressing the idea that at the beginning, people lived in perfect liberty, in a "state of nature", an anarchistic, stateless society. During that period, each person enjoyed full liberty. However, this extended liberty allowed individuals to attack the liberty of others. Thus John Locke argues, individuals came together to set up a state - an institution that holds the monopoly of power, set out to protect the natural rights of the individuals. Thus the state was set up under a "social contract", having specific tasks. If it exceeds those tasks, and becomes as institution that oppresses the natural rights of the individuals, it looses its legitimacy, and can be justifiably overthrown, so that people can re-establish the social contract.
The Treatise has been extremely influential since its publication. It established a social contract theory which examines the legitimacy and the limits of government in relation to individual liberty, making John Locke the founder of Liberalism. This is the essay that established the principle of limited government. To this day, it is still taught in university classes under a lot of disciplines of the social sciences.
In my opinion, the Treatise is outdated. John Locke begins his analysis by examining the idea that each person is born with natural rights. When he has to justify however, why he believes that these rights exist, and why they are part of every individual from the moment he is born, John Locke often provides the answer through religion. God is a character that will pop out a lot throughout Locke's short Treatise. Although such an explanation must have been sufficient for the Christian Europe of the late 17th century, I find it highly insufficient for today. In one sense, it proves that the idea of natural rights, as Locke conceived it at least, is not objective but subjective - an atheist, or a believer of another religion could very easily oppose the conclusions of Locke, which are either based on Christianity, or strongly influenced by it.
Because of this, I found the book frustrating to read. But the moment I finished it, I realised that I had gained a new world view to perceive the world around me. John Locke's book may be dense, frustrating and boring at times - but it is truly a book worth reading, and I would advice it to everyone, even if you end up disagreeing with him.
The edition is pretty good. It is both useful for general readers and students alike.