While I'm no Tolkien scholar, I am a big fan. I'm now also a very big fan of this book. After reading through I really want to run this.
First off the book clearly has a setting. It's set firmly between the Hobbit and LotR. There is information on the people who follow Beorn known as the Beornings. As well as Bard leading his people north to rebuild Dale. It's really laid out well and good at explaining the time between the major events in the books.
The Cultures, which replace races are really done well. I find enough in them to encourage players and support different story possibilities. The cultures of man are the Bardings, Beornings, Dundain, men of Bree, men of the lake, men of Minas Tirith, Riders of Rohan, and the Woodman of wildland. The non-human cultures are Dwarves of the lonely mountain, Elves of Mirkwood, and the Hobbits of the Shire.
The Classes, of the six classes provided none are magic users. The scholar has some healing abilities and some trick abilities but nothing like the spells of 5E D&D. I like the variety of classes available. They really do cover the spectrum without too much overlap. The classes include Scholar, Slayer, Treasure hunter, Wanderer, Warden, and warrior.
The next section of the book is Virtues. Virtues are in essence feats. While a few (5) virtues are open and allowed by anyone the rest of them are Cultural specific. I find 5E feats truly superior to the version in eirlier editions. I find the ones in this game even superior to those in the 5E players book. Flavorful and specific to the people of each culture.
Backgrounds in AiME is less what job you once did, and more who your character is at its core. Part personal story and part archetype.
The equipment section is pretty basic yet pretty inclusive. Included in the equipment is a section or cultural heirlooms, which can be gained through story or Virtues.
Something new and interesting added to the rules is Journeys. This is a phase where the players plan out a route. And the number of perils will be found along the way. Players assign roles to characters and roll to see how well the party does on the travel. The journey will also include encounters both fellowship and combat along the way.
Some rules added by AiME is a new Ability called Shadow and some added skills. Shadow is taint of the dark forces. It's both the mark of dark influence and a measure or sanity, as the darkness clouds the mind of the effected.
After finishing the read through I was listening to someone review another game describing it was "not just another Tolkien based fantasy". And it hit me how un-tolkien like most fantasy is. Middle earth is actually a very dark and dangerous place. Middle earth is a very low magic when placed next to any version of D&D. It's full of personal horror and corruption, well intending people who do evil trying to do greater good. And stories of the lowliest of people rising to the occasion, overcoming the greatest evils. This to me IS what I want in a setting.
I've seen a few people talk about using things from AiME to run other low magic settings. One idea I would like to add to that is everything written in The Hobbit and LotR is set in roughly 1/6 of the total land of one of two continents of Tolkien's world. It would be just as easy to introduce other material to the AiME world.
Ideas for stealing from D&D to add to your AiME game. Goliaths could be men of the north, living north of the grey mountains for 1000s of years. Genasi are elves who originate from the northern undieing lands, from the region that are elemental touched. Eladrin are elves who have lived in the southern undieing lands who are closer to elf magic. Drow are elves touched by the shadow who moved to the land east of Rhûn. There is a lot of room on Tolkien's map not fleshed out.