I should have read this book (free for Kindle) years ago. Machiavelli's works on ancient history came up frequently in a different book I read recently, and he has been cited in several other books on my lists. Alas, I've now read this work. I find some of the oft-cited passages I hear are somewhat taken out of context.
The version I read had a brief biographical sketch of Machiavelli, which was helpful. Machiavelli is foremost a historian, so he cites examples of rulers and conflicts both from Florentine and Italian history, the current Ottoman state, Greco-Roman history, and the Bible.
He starts by looking at the failures of statecraft-- how a monarch can lose a state which he has conquered or inherited. Louis XII was one such object of failure in his aims on Italian provinces. He talks of how one holds a free Republic, you either have to destroy it or make it a tributary while encouraging development of an oligarchy there to maintain defacto control. This seems like it's played out accurately in world history.
Machiavelli's "it's better to be feared than loved" is in the context of a Prince who takes a territory who was originally not his own. There will likely be unrest, so the advice is to do some large act of cruel suppression up front to quell dissent and then do small acts of benevolence over time to keep the populace pacified. If a ruler drags out the cruelty, he will breed hatred which is the ultimate failure of a monarch. The ruler must appear to be capable of both cruelty and mercy, so that he appeals more broadly, and where possible he should have an underling be the "bad cop" enforcer. It'd be best to be both feared and loved, but you will always have to give one of those up and it's best to give up love. The great projects of history, according to Machiavelli, were done by rulers who were remembered to be mean and not kind.
It's always a bad idea to rely on foreign mercenaries for your army. Machiavelli marks the decline of Rome with the hiring of Goths to do soldiering at the cost of the Roman army. France was making the same mistake in relying on Swiss mercenaries at the time of his writing. Building fortresses are of no defense when the people hate you.
A ruler has to be "liberal" in his spending. Games and welfare for the people, benefits for the standing army. This is obviously hard to do unless you're conquering and expropriating-- otherwise you bankrupt your treasury. The Prince gains glory and reputation by accomplishing big tasks-- namely conquering territories and enriching the kingdom.
The Prince should also seem to be a man of integrity. The great rulers abandon virtue when they have to-- sometimes they have to break their word in order to protect their position or the state. This is acceptable so long as not done in such a away that the people despise him. The prince should be virtuous but also know how and when to get his hands dirty.
A Prince should have a few advisors that he listens to and that he rewards for speaking honestly and openly; he should ignore all other opinion. The Prince should always make sure his advisors and viceroys know that their positions-- their wealth, authority, and very lives-- are at the whim of the Prince so that they don't go seeking their own gain or become corrupt.
A Prince is someone who believes he has the power to shape world events, that everything isn't left to "fortune" or random chance forces of history. He yields that authority and has other men follow him.
I enjoyed this book, it's obviously a 5 star classic.