Mormonism is a valid flavor of Christianity. The late Dr. Walter Martin is one of the greatest thinkers, writers, and debaters on the subject. This is an awesome debate. It's Dr. Martin against the best apologist for Mormonism at that time. This one was truly a debate for the ages. Take the time to listen to it.
Apologetics 315: Debate: Is Mormonism Christianity? Walter Martin vs. Van Hale