How does it approach adventure/scenario design?
As I read through it, and begin working with it, I think I would have to say that it approaches the whole thing from the perspective of the 10-year campaign, not the 1 day scenario. This is not to say you could not design a one-shot (I've run 2 different one-shots thus far; one at Gencon and the one out of the book) but the game, as designed, is intended to tell longer stories. The in-game time, however, can pass extremely quickly as the party travels. The scenario we were given to run at Gen-con covered nearly two months worth of in-game time in three to three and a half hours as the party traveled from southern mirkwood, up to northern mirkwood, back down and then half-way up again.
It seems to me the best method for campaign design, and this is suggested in the book, is for the Loremaster to decide what story he wants to tell. Once this is done, he can then fill in the events, as they happen from year to year, taking into account different player responses. Then, once the broad time-line is established, he can create smaller quests to fill it in. As the quests are designed, the Loremaster can also create individual encounters, both combat events and social encounters. Finally, individual locations, for exploring can be filled in and stocked with creatures.
As for individual threat levels, and how tough to make them, some of it, I think is going to be learned on the fly. Even at "1st level" however, the PCs can handle themselves pretty well so long as they are not weary.