Mostly good people trying to hear the voice of the Lord and live good lives. Man-made, God-inspired...just like all of the other religions.
The basics of the church's doctrine claims that a boy named Joseph Smith was seeking Christ's church, and during his quest he prayed. God chose him as a prophet to restore and re-establish the church as it had been in Christ's time. Since then, God has given mankind the Book of Mormon, the Doctrine and Covenants, and The Pearl of Great Price as divine books of truth. After JS, other prophets have followed, and there's one today. The church claims to be Christian and that at the center of all they do is Christ and the family. The doctrine of eternal families and becoming like God/Christ is most people's motivation for joining/staying in the church.
At its best: a very tight-knit community that provides a rigid structure for someone's life that can bring them hope and a little happiness. For the right kind of people, mormonism can be a great experience. At its worst: a man-made cult designed to feed off of the hope and money of believers.