In modern thought a Christian is anyone who believes that Jesus is the Son of God and adheres to the biblical principles of the Bible.
The Mormon organization, although claiming that the Bible is one of it's doctrinal books, is very much the "lesser" book in their view. The book of Mormon, D&C, and Pearl of Great Price all are viewed in higher light then the Bible. None of these are even recognized as inspired books by Christianity.
Furthermore, the Mormon church operates with more cultish views then biblical views. The Bible supports "love" as a central theme. Walking in love with those you come in contact with whether they are in agreement with you or not.
Look at how the Mormons handle family members who leave the church. They are basically disowned. These are not isolated cases, but you will find numerous writings of those who have left and how they were treated.
Christians also believe that the New Testament is where we live today even though we can learn from the Old Testament as Jesus can be found within it. The Mormons live more in the Old Testament then in the New. Have a "prophet" that operates as an OT Prophet did instead of how the NT Prophet operates. They adhere to a "temple" which is an OT concept instead of we being the temple of God. Within the temple of the Mormon church are many not only unbiblical things, but some very demonic operations.
Although denied by the government of the mormon organization, polygamy is still widely practiced. My wife, who grew up in "normal" cities in Utah knew several people who practiced polygamy that attended the mainstream mormon organization, not the splinter groups.
Doctrinal beliefs severally separate the mormon organization from Christianity. Some examples include Jesus and the devil are brothers whereas Christianity believes that Jesus is God manifested in the flesh (John 1) and the devil is a fallen angel. Another is that Jesus was just a man who was perfect and thus exalted to godhood, whereas Christianity believes Jesus is and always has been the Lord God Almighty. The mormons believe that not only are men and women married in heaven but that women are eternally pregnant whereas Christianity believes that there neither marriage or giving in marriage in heaven.
Oh my, this could be an endless dissertation. It is like posing the question, "Both Elephants and shrimp are living things, whats the difference between the two."