If that is your definition of "Christian", then Islam and Judaism (which you referred to before) would fit into that definition of "Christian." 
 
When the mass majority of people are referring to a "Christian" religion though, they are not using that definition.  
 
Mormonism fitting into the "Christian" Definition, no matter what that definition may be, isn't going to be the deciding factor at the "Pearly gates."  
 
What really matters is following God's Commandments and emulating Christ. Listening to his prophets and recieving the saving ordinances as proscribed by God's word.

Polytheism is generally the belief or worship of multiple gods. 
 
We believe that many gods exist (other than The Father, the Son and the Holy Ghost) however we do not worship them, we merely acknowledge there existence.  
 
The LDS church worships one God and that is God the Father. 
 
Please remember that the term Christian is not defined in the bible, but was used only by enemies of the church in reference to the followers of Jesus Christ.  
 
Are we polytheistic? I would say not, we are merely followers of Christ, according to the dictates of our own conscience.

Yes, we believe in well, multiple Gods.  
 
However, we ONLY believe in worshiping ONE God, which is God the Father.  
 
So I guess it depends on the actual defition of monotheistic. I would say we are monotheistic, because we believe all glory goes to God the Father and we fully worhsip God the Father, and no other God.