I have been using this site for a couple of years now and I have got through most of the beginner stuff. I am quite pleased because I'm not a fast learner and only have 1 hour a day to study. One thing I think that is lacking at the beginner levels is reading materials. Of course that is supplied in the form of transcripts of the kaiwa, but what I mean is practice reading materials that use the same grammar, kanji vocab etc introduced in the lessons and get the student familiar with narriative modes. There is never enough of that in published texts and none of it on this course (at least at the level I'm working on).
I am not sure why this is, but I suppose one reason might be that it's a whole lot of extra work to produce such materials without any obvious return. I can sympathise with such a perspective, if that is indeed the reason for an absence of reading materials beyond the kaiwa transcripts. However, I think I can see a way to do it which would benefit students and probably have a return as well.
You could start off by simply writing a narrative scenario to accompany each kaiwa. These narratives would strive to avoid using grammar, vocabualary, kanji etc. that were not already a part of the series, with the idea being that when someone had worked through the kaiwa series they would then be able to use the readings as review and practice instead of simplly going back and going over and over the same kaiwa again and again.
From my way of thinking this would be a way to keep dead series alive and add more content without having to expand the series content. People who wanted review could always go back to the series they had already been through and find new content - new, but not in the sense of introducing more than an absolute minimum of material that was not already in the original series. Of course, you wouldn't have to stop with the scenarios of each kaiwa, you could then branch of into related stories. OK you couldn't do that easily with every series, but there are several of them that you could.
Learning Kanji is pretty hard for me. Many do it by rote, pretty much in the style of the Japanese education system. But there is growing evidence that people can learn kanji faster by simply reading them in contexts that involve material that they already know. If the guys who run this site decided to get into this side of things seriously it might add a whole new dimension to the program and keep people coming back for more.