I'm usually better at writing negative reviews - the snark in me can be allowed full rein, then. This book does not deserve any snark.
From Hobbit to Hero was a good read. It starts with a quite fair and detailed summary of Aragorn's role in the LotR books. Well, perhaps some people might think the author was reading depths into Aragorn's character that Tolkien never put there, but I had always seen Aragorn in exactly the same light as E. Stephen shows, so I have no quibbles here.
To me, this read a lot like a book a stereotypical Hobbit would like - it has everything s/he knows already set down fair and square with no contradictions.
The most interesting chapter for me was the second one, where E. Stephen traces the evolution of Trotter the Hobbit with wooden shoes into Aragorn last king in a mighty line of kings from out of the West. I've read the HoMe volumes, but E. Stephen deftly dissects the Trotter to Strider passages out of the mix. She is as puzzled as I was when I read the HoMe volumes as to what JRRT was thinking when he wrote Trotter. There isn't a lot of change in the scenes between Bree and Moria and yet Strider is a very different character from Trotter. You'd think it would make a lot more difference in how they were written, but it doesn't. Oh, there are tweaks - Trotter the Hobbit can't physically dominate the room in Bree the way Strider the Man can - but the feel of the scenes is eerily similar and very little of the dialogue or the sequence of the action had to be substantially changed when Trotter was re-imagined.
Originally the "sequel" was to be "about Hobbits", so JRRT felt a more heroic Hobbit character was a necessity. But it never really worked (Trotter on the back of the pony while Boromir rescued all the Hobbits singlehandedly from the snowstorm on Caradhras was certainly not heroic) and it never solved for JRRT a main problem - how to integrate his love of his larger mythology into the story. By giving this character a backstory that integrated into his larger mythology, it solved a lot of plot problems, while creating a whole new set of ideas and the problems that came with them. The invention of the Second Age with all the history of Numenor and the Rings changed the focus of the myths known at the end of the Third Age from elf-centric to man-centric. Men remembered - they had an unbroken tradition to the Elder Days, too! It was partly this problem that sideway-ed the completion of the Silmarillion. The origin myths - the two trees, the creating of the sun, etc - were *mythic* and not based in what was clearly *real* even to the Men of the times. If Men had a tradition going back to the Elder Days... JRRT never satisfactorily solved this problem in his lifetime. I guess that's what fan fiction is for.
The change from Trotter to Strider took place a lot later in the writing sequence than I had remembered from my reading of the HoMe volumes. Trotter existed for 8 years or more.
The rest of the book traces Aragorn's heroic roots to the various historical literary and mythic traditions; the Arthurian of several eras, the Welsh sagas, the Greek, and the Norse, with a special emphasis on the Sigurd and Sheave legends.
The end of the book tries hard to wedge Christian themes onto the LotR story. While showing that any one-to-one correspondence between any of the LotR characters and Jesus was quite deliberately made impossible by JRRT's loathing of allegory, she makes a plausible case that the spark of the "divine" that existed in Men due to the admixture of elven and maian blood that was preserved in Aragorn & Arwen's line opened the way to a "savior" in latter days, who some thousands of years down the road would be Jesus, and thus fulfilling the prophecy that the marring of the world by Melkor would be erased by Men.
I don't quite buy it - even JRRT had to resort to "oh, we don't talk about it" in the Athrabeth rather than giving a reason why any action, or even what the action could realistically have been, by even a group of Men should irrevocably doom all Men forever - but that may be my own biases speaking here. Anyway, the discussion of these points is well-handled in the book, even if I come to a different conclusion than the author.
There is a very good discussion of Aragorn's death and how it contrasts both to Arwen's and to the "fallen" or "unfallen" condition of Men and how being Numenorean affects the fact of death.
Nothing in the book was startlingly original for me, but it is nice to have all the arguments and resources on my favorite character collected up in one place.