I find that people expect Landmark to be a social community or a way to uncover painful things about ourselves and fix them. Landmark indeed is a social community for some of the participants but the primary bond of the people involved is the transformational work itself. It really doesn't work as a typical support network or a simple gathering of friends.
I find that the biggest expectation that people have is that the Landmark courses or groups are about sharing grief or personal foibles together and supporting each other. There are many such groups but Landmark is definitely not one of them.
The Landmark approach is that each participant is a healthy, successful, and well-adjusted person who is really in need of nothing. This is certainly quite different from most religious or therapeutic approaches. This approach is so atypical that it is hard to understand unless it is experienced. Probably the best way for a person to assess the value of a Landmark course for themselves is to listen to the results that others have gotten. If those results are something that seem worthwhile, I would suggest that taking one of the courses would be a good idea.