I finished reading it yesterday. As pointed out, it basically dismisses LOTR as a tissue of propaganda, misinformation, and Elven coverups (eg. the pirate fleet was actually a hired merchant fleet, whom the Elves bribed & threatened into silence, at which point rumors went into operation).
I'm not hugely fond of taking that kind of out - it bothers me that Eliezer takes as many liberties with the Harry Potter canon as he does, I really like the single-point-of-divergence style and regard multiple points as inefficient/inelegant.
But the story makes up for it as it morphs into a John le Carré spy novel culminating in an excellent double or triple cross.
Would I call it rationalist? Not especially, not more than your usual spy novel with its tradecraft and trickery.
No, it's not especially rationalist, even as the heroes' people wear that label. It's pretty much a spy thriller. Doesn't give the reader a fair chance to see the characters' clever rational moves ahead of time, so not "rationalist" advocacy except maybe very broadly.
I must say, I'm enjoying it a lot more than LOTR. Loved the movies, was nagged to read the books by loved one, made it all the way through (except the appendices), have no intention of ever doing so again.
This may be old news to some people, especially the Russian speakers, but I didn't see an article about it here.
In 1999, Kirill Yeskov, a Russian paleontologist, wrote The Last Ringbearer, a 270-page take on Lord of the Rings from the point of view of a medic in Mordor's dying armies who is also a "skeptic and a rationalist." In fact, Mordor represents the forces of reason in this retelling of the story. As a Nazgúl (himself a former mathematician) explains, Mordor is "the little oasis of Reason in which your light-minded civilization had so comfortably nestled." Barad-dur is "that amazing city of alchemists and poets, mechanics and astronomers, philosophers and physicians, the heart of the only civilization in Middle-earth to bet on rational knowledge and bravely pitch its barely adolescent technology against ancient magic."
The story has been newly translated and is available in free PDF form -- in English and the original Russian. There's a recent review from Salon as well.