Seventh Day Adventism would not be considered a full blown cult because they are Trinitarian. However; they have several cultic doctrines:

1. Obedient Christians will always observe the Saturday Sabbath.

   1. Paul clearly says not to allow anyone to judge another on this issue (Col. 2:16) They do not really kept the Sabbath as Moses commanded, with all the rituals. Sabbath candles, Hebrew prayers ect. All they really do is take Saturday off.
   2. Most hold to the doctrine that if you go to church on Sunday that is taking the mark of the beast. So they are the only ones who will not go to hell. This is very offensive to Christians and Paul says this is a very serious sin against the body of Christ. (1 Corinthians 1 and 3)
2. They other legalistic practices such as not eating pork, or using alcohol and tobacco and to sometimes coffee and soft drinks that contain caffeine.
3. The Majority still hold to the teachings of Ellen G. White. Considered a false prophet by Christians, she supposedly had visions from God that contradict the Bible and history.

Links for further study:
http://www.ellenwhite.org
This site shows the truth about the supposed prophet/visionary Ellen G. White

http://www.sdaoutreach.org
This site has lots of general info on the Seventh Day Adventists