Hello, I am a member of the LDS church. The reasons I have been given for us to not be Christian are debateable. I happen to believe I am a Christian, so take it for what it is worth to you.
The LDS believe in the doctrine of works along with faith in the Lord Jesus Christ. We do not believe that we can sit idle with a belief in Christ and be saved. We do believe that man is saved by the grace of God, but that we have to be worthy of that grace by doing good works to glorify God, not ourselves. Many say that we are wrong because of the whole works part, but there are many scriptures that say through grace and many that say faith and works. You decide.
We also, as a core belief, have the doctrine of a Godhead, not a trinity. The Godhead is made up of God the Father, the son Jesus Christ, and the Holy Ghost. We believe they are one in purpose and one in unity, not one in personage. It is something that is open for interpretation, because there are many scriptures that can be used to support both.
We believe in the Bible along with the Book of Mormon. We believe them both to be Holy books. Many say that the Bible is the only and final work of God. There are no other scriptures. The Bible says there are sheep that are not of this fold. Also something that is obviously theorized by the Christian community. We believe that refers to the people on the ancient American continent. Thus, the Book of Mormon.
There are many beliefs that differ, but one thing in common. Christ. We believe in Christ. He is our savior. We are a faith centered on the atoning sacrifice of Christ and what he has in store. We believe in a living prophet to guide His church in these days full of turmoil. We believe in Christ, but we are shunned by fellow Christians.