Yes, I would say they are a cult.
They may not have a single, charismatic leader but the have a very small group of elder men who preside over the whole thing and dictate everything. They are the "faithful and discreet slave class" and, basically, have a hotline to Jehovah, so whatever they say has come directly from God.
They have a special language designed to unite believers and keep out outsiders, also to give themselves more legitimacy - calling themselves The Truth, for instance - everyone else's belief is a lie
They separate you from family and friends who do not believe
They cut you off completely if you leave
They use apocalyptic teaching to keep a hold of you
They have a whole history of end of the world prophecies which haven't come true, so they have had to cover their backs countless times
They change their teaching all the time under the guise of New Light - i.e. God makes stuff known at the right time and the new revelations take the place of the old, wrong ones, which were apparently, misunderstood by the leaders at the time because they weren't ready for full revelation.
They dictate the minutiae of their member's lives, everything from how to cut your hair to what books to read or music to listen to. Even very small things like not clinking glasses in a toast or saying "bless you" when someone sneezes
Most Jehovah's Witnesses are lovely, kind, sincere people, who truly believe, many others, though, are scared to leave because they will lose their entire social and spiritual network, they may also lose their entire family. It's also pretty much a life of guilt and uncertainty, because you never know if you are "saved" and will survive Armageddon until it comes and you are standing before the judgement seat, justifying yourself and all the decisions you have made. Have you sent an inappropriate card with a Bible verse on it to someone, have you read the wrong books, did you masturbate, did you go on dates without a chaperone, did you fail to spend enough hours in the preaching work, did you let your kids play with non JW children, did you attend enough services, did you put the Truth 1st in everything you did....?
It's a religion with very little room for Grace and a lot of space for Judgement.