"Cult" has become a pejorative that people apply to religions that they simply don't like, but if you can get past that connotation, Jehovah's Witnesses share a lot of traits with other high control groups.
1. It is very easy to join a cult, but surprisingly difficult to get out of one with your dignity intact. Cults do not recognize a legitimate reason for leaving. People who leave for reasons of conscience are labeled as "evil" and "mentally diseased."
2. Cults attempt to isolate you. A person joining a cult will be encouraged to break off all past associations. Friendships a person may have had their entire life are expected to wither away and die. After a few months, friends become very concerned about the individual who has joined a cult, because they don't even seem to be the same person anymore.
3. Cults attempt to control every aspect of your life, from medical care to leisure time, to education, to acceptable sexual practices. Sometimes there are sanctions, both written and unwritten for noncompliance
4. Cults attempt to control your access to information. They minimize or discourage access to outside sources in favor of their own internally generated literature.
5. Cults invent their own jargon. Their speech is littered with esoteric expressions and buzzwords that have special meaning to other members of the cult.
6. Cults rely heavily on fear. Fear of the outside world. Fear of invisible spirits. Fear of leaving. Fear of being branded and shunned by the group.
Jehovah's Witnesses exhibit all these traits. In spades.