Some of the major developments to note in this volume:
-tHere we see the final change of our friend Trotter the wooden shoe wearing hobbit-ranger to the figure that would eventually become Aragorn, son of Arathorn, heir of Isildur.
-tSaruman emerges as a figure in the text (already a traitor), though still in a fairly minor role compared to the one he will occupy later.
-tLothlorien and Galadriel emerge seemingly from nowhere, an important development indeed given the central place Galadriel would come to occupy in Tolkien’s mind (to the point where he would go back and re-write huge segments of the Silmarillion material so she could be included…though that is not even hinted at yet).
-tGandalf is gradually raised in stature from the little old man who happens to be a wizard we saw in the original version of The Hobbit to something much more (though the concept of the Istari is not yet in place).
-tRohan and the society of the Riders developing out of whole cloth with obvious nods to Tolkien’s love of Anglo-Saxon culture and literature (esp. Beowulf) being apparent in their genesis.
-tSome fun tidbits: it appears that Gandalf’s fall in Moria and subsequent return were part of the plan from the beginning; since we still have no Arwen the initial plan points to Aragorn falling for Eowyn when he meets her in Theoden’s Golden Hall (great vindication for numerous fan fic writers out there no doubt); Boromir was at first going to be an unremitting traitor who didn’t heroically die at the hands of Orcs while trying to save Merry and Pippin, but who would actually have been a full rival of Aragorn as the two vied for control of Minas Tirith.
Required reading if you have read the preceding volume and want to know how the story further grows and develops, but definitely not the point you want to start with the HoME series.