I read this bassackwards. I read The God of the Hive ages ago, which is the sequel to this book, which ends on a cliff-hanger. The worst part is I don't remember what happened at the end of The God of the Hive! Meaning, I just read a story for which I technically have no conclusion in my head.
Besides all that (guess I better go back and check out The God of the Hive...), I have ambivalent feelings about this book, The Language of Bees, because it has so little of Mary and Sherlock together. I've made that complaint about other volumes in this series before, but for some reason in this volume there's also a severe lack of affection between the two that depressed me. One of the best parts of this series is the incongruous love affair between a 20-something year old and a 60-something year old (and, of course, that it's Sherlock!). It's a clear assumption that this marriage is something very different for the 1920s, but it's also a clear assumption that it's not just a partnership - that's been made very clear over the series. So, show us the affection! In this volume, I don't think they touch each other once. That's just sad.
In terms of description in the story, my favorite part was absolutely the plane ride, but also the rendering of Mycroft's personal space which I don't think we've been privy to before.