One of the great historical books ever written. Also one of the most accurate... of course, it has the advantage of being part of the divine canon of Scripture and thus is inerrant, inspired and infallible.
The book has three main characters - Samuel, Saul and David. Many other supporting characters help provide us with a very compelling, historically accurate, account of an exciting time in Israel's history.
Spiritual lessons abound - sin is condemned, righteousness exalted, and God glorified. Read it, love it, enjoy it, and learn from it.