A lot of people, EX-JWs, believers and unbelievers alike, think that JW's are just a somewhat kooky brand of Christianity. Is it possible to "try and follow Jesus" and not be Christian? What exactly makes someone a Christian? And, what exactly makes someone NOT a Christian?
I like to make things simple, if they can be. So here is the simplest reason why all Bible Cults are not Christian.
They violate the New Covenant Jesus offered in Matt. 26: 27 & 28 (one way or another)
The term "New Testament" literally means "New Contract". The contract was for the purpose of forgiveness of sins as the above verse so clearly states. The contract is solely between Jesus Christ and the New Contract believer. It is a VERY simple agreement.
However, the Watchtower says that the New Contract is for government positions, not for forgiveness of sins.
Furthermore, they have stated that the contract is now virtually closed to believers, although it used to be open to "whosoever".
But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. Gal. 1: 8
Instead, they claim that the "light" that get brighter is new doctrines, where association with the Watchtower is what guarantees you passage into the Kingdom, not identification with Jesus. This is not the "good news" that the apostles preached. According the Gal. 1: 8 - the good news message cannot be changed, therefore they are specially cursed for this and are not Christian.