I read the Hobbit for the first time in many years, to my nieces at their bedtime. This is what I learned. Ah, note that none of these observations are original; this is just "stuff I noticed" having not read the book for a few decades.
Bilbo gets concussed. So if you are remotely familiar with Tolkien, you know he is a bit detail obsessed. Still, I was surprised to notice both times Bilbo takes a blow to the head, he actually shows signs of a concussion after. (The first time he's knocked out for an unknown length of time in the goblin caves; later he takes a rock to the head during the battle of the five armies.) That second time Bilbo is blacked out all night and till morning the next day. What's more, Tolkien even throws a line or two in on how Hobbits can recover from things like head trauma much faster than you'd expect.
It's a small thing, but I always appreciate any time media remembers that getting knocked out is like, super bad for you.
Three magic races of birds. The giant eagles, the magic thrushes, and the magic ravens. Everyone remembers the first, but the other two are necessary parts of the plot. The ravens speak English, while the thrushes help the party find the secret door, and are the information conduit to let Bard know when to aim. The Thrushes speak their own language, but Bard thanks to his bloodline understands it. Speaking of...
Bloodlines for all. It's a very old, valid criticism of Tolkein to point out in his works your ancestry not only determines your skills, it also determines to a great extent your goodness and badness. I'm very familiar with this. What surprised me was that even aforementioned magic races of birds get a genealogy, like "oh, they are the **noble** ravens, descended from such and such."
Tolkien is good at battles. While he's definitely hazy about how geology works (mountains are just magic places were stuff happens) he has a very good eye for battles. The Battle of the Five Armies (spoiler!) has contemporary tactics (describing vanguards, flanks, etc), and for the most part is just this big chaotic event most of the characters participate in but are not central to. Bilbo wisely nopes out of it entirely early on. In retrospect, this makes perfect sense, since Tolkien must have read many accounts of ancient battles [to say nothing of Tolkien serving in World War 1.]
Riddles in the Dark is obsessively plotted. Tolkien to repeat myself, was all about the deets. That said, Riddles in the Dark is kind of amazing, since every step in that chapter is carefully plotted, but often Tolkien will consider "well why didn't this happen instead" in the text. For an author who has been noted for using Deus Ex machinas, Riddles uses a very down to earth psychological realism to get Bilbo the ring, an riddle contest with Gollum, and Gollum inadvertently leading Bilbo to the cave labyrinth's exit.
There are four Dwarves. Those are Thorin (leader), Balin (older, wiser), Fili/Kili (younger), Bombur [fat]. I think the rest of the dwarves exist simply for when their numbers matter (meeting the dwarves in Chapter 1, getting help from Beorn, etc.)
Encounter with Smaug: still awesome. I mean, first this dragon howling with laughter at the idea of anyone taking vengeance on him, and then "my armor is like tenfold shields, my teeth are swords, my claws spears, the shock of my tail a thunderbolt, my wings a hurricane, my breath death!" That's worth about 20 minutes of CGI right there.
