The New Kadampa Tradition is a cult formed from the Buddhist religion. It is a cult based on reincarnation and the belief in karma. Any religious belief that does not believe in the One true God and the redemption of sin through the blood of Jesus Christ is, in my opinion, a cult.
Depending on how you define cult, all religion could be considered a cult. They all ask for some form of donation or sacrifice from a person. All religions ask that a person base some idea on faith rather than logic. All religions have a leader of some sort that is followed and worshipped almost to the point of being a deity. This includes Buddhism, which is the basis of NKT.
The New Kadampa Tradition can be designated as a cult because it brings a diverse group of people together in one thought and one purpose. They practice Buddhist traditions in mediation and chants and attitude, but they focus in on peace. A cult is not always a bad thing if the people in the groups are doing things that better the world.
No, the New Kadampa Tradition is not a cult, because it is similar to the rest of Buddhist teachings. The New Kadampa Tradition focuses primarily on meditation. The Tradition follows a variety of traditional Buddhist teachings, along with a few variations. But there is no variation that is so great that it becomes a cult, instead of Buddhist teachings.
Much like Christianity there are many branches of Buddhism and the New Kadampa Tradition is simply another off shoot of Buddhism and it should not be considered a cult. The followers of the New Kadampa Tradition still follow the basic tenets of Buddhism, for the most part, and are not necessarily following anything that is found to be out of the ordinary for Buddhism.