Although the duck-billed platypus has a bill like a duck, when we examine the rest of the animal we can clearly see that it is not a duck. Only the most superficial examination of the platypus would result in the conclusion that it is a duck.
In a similar fashion, only the most superficial examination of Mormonism would result in the conclusion that it is "Christian". The Christian Apologetics & Research Ministry (carm.org) examined Mormonism at length and identified several non-Christian doctrines that Mormonism teaches including:
G-d used to be a man on another planet.
G-d resides near a star called Kolob.
G-d, the Father, has a body of flesh and bone.
G-d was once a man but was exalted to godhood by the god of his original planet.
There are many gods. After being a good Mormon, men have the potential of becoming gods themselves.
G-d is married to a goddess wife and has spirit babies that become humans.
At the center of the Christian faith is the real, physical, historical person of Christ: the Messiah of Israel.
If a person has Buddha at the center of their faith then they aren't Christian: they are Buddhist.
If a person has an individual at the center of their faith who does not fit the Scriptural and historical person of Christ (i.e. a "christ" who is the spirit brother of Satan like Mormonism teaches) then they are not Christian.
While every Christian denomination disagrees on various points with other denominations, all of them agree on this: Mormonism is not Christianity.