Sorry Aran, contentious post coming up. I guess this thread is giving you food for thought anyway, so here we go. It highlights what I remember trying, rather unsuccessfully, to formulate and articulate to you at one point in Caernarfon. (While trying to justify that I'd never managed to listen to the accelerated listening exercises.)
It worries me that, although the current model makes the process even more accelerated for a lot of people, it may be at the cost of making it more uncomfortable and less enjoyable. It would be a real shame for that to affect retention levels. With the original model, you already had an idea that was proven to work, and was significantly accelerated compared to traditional methods.
Of course I've witnessed some people's meteoric success with the current method, which seems to work even better than the Courses if you're cut out for it. (I would hate to use the term 'learning styles' as I don't believe in them either...)
I was quite a traditional language learner, and tootled through the Courses in about a year with multiple repetitions and use of the pause button, as per the advice at the time. It was an entirely pleasurable and satisfying experience - after which I could basically talk Welsh, which was wonderful.
I don't know how many other people have experienced the same kind of reaction as @Eigentime, and if they may have been better off with the original kind of approach. It would be interesting to know about retention levels for both - I guess it would be difficult to get any kind of reliable statistics. But as I said earlier in this thread, I'm not too confident I would personally have been able to stick at the Challenges in current form, without any prior background.
I don't know the answer, am just being devil's advocate. (Will now go and hide under a rock.)