Kind of a cowboy tale, as the title suggests - and we already knew from the trilogy that Lee Scoresby was in that mold. The general appeal of this novelette (novella?) is obvious - it takes us back to the His Dark Materials universe (I use that word advisedly in this context)...the particular (subsidiary) appeal is equally apparent - it recounts the first meeting between Lee and Iorek.
Anyway, it's got a bit of energy to it - yeah, it's pretty good. But ultimately more a deepening of the original pleasure of the main trilogy than a particular delight in its own right, I think (although of course the whole point is that it's impossible to tell).