I must have owned something by Nielsen as a child since these pictures seemed really familiar, but he hasn't crossed my radar as an adult - not surprising since, as the author bio in the book delicately puts it, he "died in reduced circumstances" (in 1957) and his wiki entry notes that his pictures couldn't be given away. Which is baffling & bizarre since they're utterly utterly beautiful, far more so than Rackham & the others. (Also, do I detect an ukiyo-e influence?)
The re-tellings are very well done too, much better than a lot of this kind of thing.
Destined for the niece, we'll see how it goes.