Goodness I can't wait for the eventual Adventures in Middle-Earth "2nd Edition" when Free League finally decides to do it. They are such great books to mine/cherry pick stuff for your 5E games. I use the stat blocks in them for like most of the more "mundane" parts of DND, like the Farmers, Town Guards, Bandits/Thugs, and others for like the various villages and big no name roads/paths in my 5E games. Likewise, I really like how in other books, such as the Rivendell Region Guide and the Loremaster's Guide, they have Enchanted Qualities like "Keen," "Smiting," and what not that you can add to weapons/Armors. The Elven-Crafted Enchanted Quality, even throws a bone to the 5E Medium Armors category by allowing Medium Armor using PCs to add their full DEX modifer, ala Light Armor, to their AC class. Of course, finding something like that or having somebody craft it is another story altogether/DM fiat.
Likewise, the various Creature Abilities that a couple of the books have, can REALLY help with customizing your 5E monsters. From adding Legendary actions to monsters to even one that makes a PC Auto-Fail one of your three Death Saving Throws upon hitting 0 hp for the first time in battle. Of course my personal favorite of said abilities is Dwimmerlaik which is unique to the Nazgul. It pretty much allows any Nazgul, when you score a Critical Hit against em, to use their Reaction to basically legit go NO and Reflect your entire Critical Hit right back on the PC, that scored it, if said PC fails a DC 16 STR saving throw**. Oh and if you don't have a magical weapon, your weapon completely shatters/is destroyed on the spot. (Magical Weapons don't shatter, but your character experiences a sharp cold pain of dread that shoots through your body, causing the PC's arm to drop the magical weapon. Which means you have to waste an action picking it up/ risk DM being the type to have the Nazgul kick it away from you.) It's a bit nasty in theory and I absolutely love the idea of the theoretical look of *Uh crap on a player's face if an unlucky PC falls victim to it.
***DC 16 STR saving throw too low for Barbs/STR characters you say? DM: Laughs in changing it to something higher or a different stat when adding Dwimmerlaik to a homebrewed monster.
Really an absolute sin Cubicle 7 lost the license. They were really doing some great stuff with it and even helped the Social and Exploration pillars of 5E even more with Audiences and Journeys. And Moria would have been epic, especially since that means we would've gotten the Balrog with it as well and that would've been sweet.