You know, a lot of times fictional letters don't come off as letters someone might actually write. Same goes for diary entries. They have the wrong level of detail, too many fully-transcribed conversations and such.
Not so here. There's only one conversation included, and it's short and important. Everything else reads precisely like a chatty, newsy letter between friends. Is this because the majority of these stories and novels are told as Dr. Watson's reminiscences anyway, so it was pretty easy for Doyle's writing to slide into Watson writing letters? I don't know. I just know it's well done.
I like how Watson alludes to their very first adventure together, when Holmes insisted he didn't care if the sun went around the earth or vice versa. That exchange always tickles me in A Study in Scarlet, and I'm amused to have it pop up here.
Okay, so we have Sir Henry interested in Beryl Stapleton, and Mr. Stapleton objecting, adding another layer of mystery. Watson's rather a shrewd observer of character, isn't he? I love how he describes Stapleton as having "a dry glitter in his eyes and a firm set of his thin lips, which goes with a positive and possibly a harsh nature" (p. 630). No wonder Holmes is trusting him to observe things and send back facts! While deducing from facts is not Watson's strength, observing people certainly is.
The bit about Dr. Mortimer being filled with joy over digging up a skull amuses me. Can't you just imagine him, beaming with pride as he shows it off to everyone at lunch? Also, Mr. Frankland of Lafter Hall is a very silly fellow, with his litigious habits. Watson says that other than suing people all the time, "he seems a kindly, good-natured person" (p. 632), and I like to imagine that Lafter Hall often rings with laughter. Especially since Watson also says he "gives a little comic relief where it is badly needed" (p. 632).
And then we end with Watson, the not-so-sound sleeper, waking up because he hears noises in the night again and discovering Barrymore creeping around with a candle. Spooky way to end the letter and chapter!
The longer one stays here the more does the spirit of the moor sink into one's soul, its vastness, and also its grim charm (p. 629).
Possible Discussion Question: Why do you suppose one page is missing from Watson's letters to Holmes? Why does he specify that? There's no point in this letter where he says, "And I'm missing a page here, but I'm pretty sure it said thus-and-so."