The Jehovah's Witnesses are a dangerous, anti-Christian cult. They deny many of the essential truths of the Christian faith. That is what prevents them from considered as merely another denomination of Christianity (like the Baptists, Methodists, Presbyterians, etc.).
Christian doctrine falls into one of two categories: essential and non-essential. There are certain things that a person must believe in order to be considered a Christian. In that sense, they are essential. The Apostles' Creed is a good summary of essential Christian teaching. To this one could add the gospel of grace, justification by faith alone, and the doctrine of the Trinity. The list of essentials is relatively small, but extremely important. It's the core around which the vast majority of Christian denominations are united.
The non-essentials are those doctrinal matters over which well-meaning Christians can disagree. So long as they are united on the essentials, there is freedom in this area. Non-essentials include such things as speaking in tongues, infant baptism, church government, and so on. Believers may hold strong opinions on non-essential matters. Non-essential doesn't mean non-important. Even so, Christians should not divide or break fellowship over these things.
Rupert Meldenius, a 17th Century peace-loving Lutheran, offered this advice: IN NECESSARIIS UNITAS, IN DUBIIS LIBERTAS, IN OMNIBUS CARITAS. Roughly translated: "In essentials, UNITY. In non-essentials, LIBERTY. And in all things, CHARITY." If the Christian church would take Meldenius to heart, it would be a much more unified body.
The Jehovah's Witnesses, in rejecting essential Christian doctrine, places itself squarely in the realm of heresy. There is no chance of unity with the body of Christ. From its Arian Christology to its Pelagian soteriology, the WatchTower seems to be repeating all the gross errors of the ancient church. As they say, those who refuse to learn from history are forever doomed to repeat it. Until the WatchTower repents of its heresies, it will remain outside of the Kingdom of God, an enemy of Christ and of his church.