Being a free Kindle edition there is no introduction and no notes - but you do get the full text. The only difference from the original is that there are fewer capitals and italics. Hobbes used them for emphasis very much more than a modern writer would, and their pruning in this edition makes the text easier to read.
Modern political philosophy begins with Hobbes. Before Hobbes, writers for centuries had accepted the divine right of kings or did not think much about the origins of government. Hobbes provides reasons as to how and why men come together to form government. He starts with the assumption that that the organised state is a choice. The alternative is the "state of nature", where there is both a "right" of nature and "laws" of nature. Hobbes uses these terms in a very individual way. The "right of nature" is "the Liberty each man hath, to use his own power...for the preservation of his own Life". The "laws of nature" dictate that each person should seek to live with others in peace, and should only retain the right to as much liberty as he is willing to permit others. These "laws" are found by reason, and are utilitarian rather than moral. Hobbes is simply saying that if men think about their situation, reason tells them that giving up their natural rights in exchange for others doing likewise is the best means of self-preservation, even though it is contrary to human nature.
On human nature Hobbes is cynical. Reason suggests advantages stem from co-operation, but this is outweighed by instinct. Men are fundamentally competitive and selfish. They are also roughly equal in ability so no one person can impose his will on others, and so the most one can hope for is to protect oneself from others. Life in the state of nature is "solitary, poor, nasty, brutish and short." Men are therefore driven to create government via a pact with others to give up their natural rights to a sovereign authority, which may be either an individual or an oligarchy (Hobbes prefers the former). Hobbes uses the concept of a "social contract". It is not an historical event but a logical device to describe the ongoing basis of consent to government. Hobbes' view of human nature is such that he allocates absolute power to the sovereign. Limited government, he believed, is unworkable for men are too prone to division and selfishness, and "a kingdom divided against itself cannot stand." Hobbes was influenced by the religious and political divisions preceding the English Civil War. Hobbes wishes the sovereign to have the power of censorship, including the ability to prevent discussion of religion because he believed that such discussion leads to conflict. Anybody seeking to preach a new religion should be treated as a criminal.
Is there an ultimate right of rebellion against the absolute ruler? The answer is to be found in the nature of the social contract. Men give up their natural right to self-preservation to a sovereign in order to to better achieve it. If a situation arises where the sovereign cannot ensure that safety then society is dissolved. Can any action by the sovereign be challenged? Yes, if a man is conscripted into military service (an obvious threat to life) in circumstances where the survival of the state is not threatened. If the survival of the state is threatened then so are the lives of its citizens, and in these circumstances the sovereign can impose conscription. Hobbes adds that even in this case a citizen should have the right to replace himself with a volunteer if one is available.
"Leviathan" is not an easy book, not helped by the fact that the English is that of a man born just 24 years after Shakespeare. However, it is an important work that makes a good study companion to Locke's "Second Treatise", which argues for limited government.