I've asked this question myself.
Whereas I can't offer a definitive answer, I can say that I've noticed it to be what people often call "a poor cousin" of traditional religion.
Historically religions defend ancient traditions as
unchangeable truths, but Jehovah’s Witnesses seemingly create their theology ad-hoc to
protect their central belief that they are the one-true religion approved by
the Creator. It often appears that all that really mattes to them is that they have found the truth, and that what they believe is true without any possible room for mistake. The have and will continue to change their definition of the last days and the final generation "as-needed" to protect this, even though what they now teach would have disfellowshipped each and every member of the Governing Body for proclaiming it in, say, as recent as 1985.
Tradition, ritual, spirituality, and a sense that there is something more transcendent and mysterious, greater than ourselves dominates religion. But the tableau offered by the Witnesses is a dry wasteland by comparison. There are no list of heroes or saints who defended the faith from changing or altering course. There are no other-worldly epiphanies or theophanies or miracles that they claim ownership of. There is no meditation or contemplation. They use the Bible like the Gnostics of the past and the Mormons of the present, advocating that divine revelation is limited to a written text instead of from the mouth of a deity.
Most Christians I know do not consider Jehovah's Witnesses fellow members of the Christian faith. The central tradition of Christianity is rooted in the belief that the Creator appeared incarnate, becoming human in order to be more relate-able to the humanity he created. The belief that Jesus is not this ultimate revelation of God really puts up a wall between the Christians I've known and the Witnesses. But some do feel as you mentioned.
I would put my money down on the Jehovah's Witnesses being more of an ideological movement than merely a religion. Like ISIS, Nazism, Imperial Japan, and other similar movements of the past, the Witnesses have religious overtones mixed in with a world-domination theme, looking forward to an end of present society and all its institutions, propagandizing a new world order to come in its place with them on the top and in the middle. The present society is worthless and less-human than they are, and it's an "us-against-the-world" philosophy that fires up the zeal of their adherents more than anything else.