The basic definition of cult is simply a religion with its rites.
"a particular system of religious worship, especially with reference to its rites and ceremonies." http://dictionary.reference.com/browse/cult
However, people tend to think of a small crazy group in a commune. Due to this range of perceived definitions, the word cult has lost its usefulness. For that reason, the term used now in such discussions is whether a group uses "undue influence." That way the discussion can focus on the way the group operates, and the affect on the followers, rather than the collapse into a debate on doctrine.
Watchtower complies with a lot of the practices that are considered undue influence, in particular not being able to question the leaders, and shunning.
Jehovah's Witnesses vary greatly in how strictly they follow the rules and internalize the doctrine. For many that just hang in there for social reasons, it does not hold much influence in their life. For those in Bethel, it is very much like being in a small cult commune. Once they move to Warwick, that will become even more evident. When I was in Sydney Bethel, which is in a country setting an hour from the CBD I felt like I was trapped in a cult commune, and found it oppressive and depressing.