A pretty well balanced review of Landmark can be found
here
This review almost makes me want to try it, if only to observe my own reaction to it.
My knowledge of Landmark is limited, but my roommate back in Seattle was into it so I know a bit about it. From our discussions, I came away with the impression that the program had more positive aspects and less negative aspects than a cult like Scientology typically would. However, it did seem to be a lot of fluffy mumbo jumbo to me but then I guess there is a big market for simple heuristics repeated ad nauseum.