What was not clear when I first heard about ngöndro is why it exists. It is not primarily intended to be a life-long practice, although some do it. It is not something you have to do or that everyone does. It is purely remedial, a simple remedy, but for what? It sounded like a trip to the woodshed when I first heard about it.
Personally I think the choice of the word "remedial," with its negative connotations, is perhaps a poor choice. Those who chance across this may begin to think "I don't need remedial work... I need to move forward, not backward!" The first two practices (Refuge & Bodhicitta and Vajrasattva) are to purify obscurations, and the second two (Mandala and Guru Yoga) are to gather merit. These two processes (purification and accumulation) are things I think we all can see a use for, rather than feel like we're wearing a dunce cap and sitting in a corner while the cool kids get to play.
In fact, in Tibet, dharma students often do ngöndro BEFORE they ever try to seriously meditate. Think about that please. Perhaps the only reason that here in the U.S. we first try to learn to meditate is because ngöndro is too difficult for Americans to contemplate. Yet we are very comfortable with various physical exercise programs. Well, ngöndro is essentially the same thing, but it is primarily a mind-exercising regime, as in: the mind is something we also have to get in shape and learn how to use.
Here I think it is worth noting that it isn't just Americans choosing to do shamatha & vipashyana before ngöndro, but arguably just as much a matter of emphasis on the Lama's side. Several Tibetan teachers have made a point of mentioning that "Westerners" don't have the cultural baggage that Tibetans do, and that this means they can more readily jump in on those meditative practices. Some have even gone as far as to say that it was a fault of the Tibetans that they didn't strenuously engage in these, choosing to rely on lamas to do pujas, etc. Dzongsar Khyentse Rinpoche and Yongey Mingyur Rinpoche come to mind here.
Otherwise I think it's a pretty good intro, all in all...