One of the most powerful tools used by Mormons to discredit traditional Christianity is the concept of the Godhead.
Mormons have a description of three deities: the Father, the Son, and the Holy Ghost, each of whom has a distinct history and ontology. This is, I believe, much easier to understand than many of the descriptions I've heard of the true God of the Bible, the true Trinity described (no, not named such I will admit) in the Bible.
The problem isn't with the truth of the Trinity. The problem is that many Christians unwittingly misuse the name of God — by limiting the use of that name to the Father alone. True, the Father is God. But so is Jesus, wholly and completely God. And so is the Holy Spirit.
Here's a diagram that helps me a lot with this difficult concept:
