Howcultswork.com
If you go to this website you will find that the Watchtower meets every criteria they list. Not that this particular source is the absolute authority on cults, but it's hard to deny that the Watchtower uses the techniques listed there.
Most people think to be a cult means everyone has to live in a commune and wear distinctive clothes. While some cults do that, what defines a cult is the methods they use to retain and control their members that makes it a cult, not the outward appearance.
While you could say every religion is a cult, most mainstream religions do not engage in these practices:
Information control. The Watchtower discourages its members from seeking higher education or reading literature that is critical of the organization. They constantly warn about the dangers of so called apostates, saying they are bitter and angry and tell lies. Any former member who criticizes the Watchtower is considered a "bitter, angry apostae". Most religions have no problem with higher education, reading things not endorsed by them or even talking to former members, even if they are critical of the church.
Relationship control. JWs are discouraged from seeking relationships outside of the organization, they are absolutely forbidden to talk to disfellowshipped former members. The vast majority of religions have no such rules.
Deception. Does the Watchtower tell new recruits that they have incorrectly predicted the end of the world numerous times? Do they tell new recruits they will be disfellowshipped for celebrating Christmas? That they will be expected to shun their children if they do not choose to be JWs if they were ever baptized? Most religions are open about their beliefs, practices and history.
Fear and intimidation. The Watchtower claims to be the sole channel of communication between God and mankind. To disobey them is equated with disobeing God and will result in death at Armageddon and shunning by family and friends. Most churches have no problem if you leave their church and join another. While some may believe in hell fire or that they are the only true church, not all do.
Reporting Structure. Jws are encouraged to report transgressions they know of to the elders. Things told in confidence are shared with other members, judicial committee are formed, the Watchtower is informed in all cases of serious sin, a record is kept on file for years. Individuals are controlled by the elders, the elders report to a circuit overseer, they report to the Watchtower. Meeting schedule and content are tightly controlled by the Watchtower. Kingdom Halls are no longer owned by the congregation, "mother" decides which halls get built, which are sold (all profit to the Watchtower) which get remodeled. Most congregations on other religions have much more autonomy, membership often decides to builds the church and decides who will be their pastor. That pastor decides the content of sermons each week and tailors his services to the needs of the congregation.