1.  First reaction:  Shock.  Disbelief.  Utter befuddlement.  Second only to the shock I received later at Mt. Doom, when Frodo, who I'd identified with completely, did the unthinkable.

2.  How does the action sequence suceed/fail?  As I've mentioned several times, it works, in part due to Tolkien's masterful choice of active verbs, gerunds (which continue the action), and sentence length/rhythm, as well as powerful image-words (blank darkness is used at least twice) to set the tone.  A great vocabulary and solid previous character development doesn't hurt, either.

3.  Tolkien is amazing.  As you note, normally the sentence you quote ("He staggared, and fell, grasped vainly at the stone, and slid into the abyss.") would either be cut into several sentences, or would be punctuated with fewer "and"s, as it appears to be a list.  But what he does really makes the reader feel all of this in continuous action slow motion.  Wonderful.  Language, mechanics, syntax, style....all can be harnessed to give us some amazing "scenes".  Who needs movies?

CHALLENGE

How many times does Gandalf use the term ‘fool!’  Show your work.

Sounds too much like math to me. *shudders at the thought of LotR story problems*

Not all those who wander are lost.