I’m another Murata newbie (@jhol did a good job promoting this book club, I think) and I’m going in completely blind. I just finished this week’s part and it was a very enjoyable read!
Murata indeed has a very straightforward writing style (in this book so far) so I only have vocabulary to worry about and that’s not such a big deal with the e-book version.
Like @jhol mentioned, she paints a vivid picture with few words and I think that that is what makes it so enjoyable for me.
It might have been the opening sentence
. I just couldn’t figure out what she meant with 夜の欠片 (it became clear later) and I couldn’t figure out if 秋級 was a normal noun or a proper noun because I couldn’t find it in a dictionary and also not on Google Maps. In the end I just settled on it being either a fictional mountain or a mountain that is so local that it isn’t listed on Google. (Feel free to correct me if I’m wrong.)
I’ll admit that I also had to do an image search to figure out what a 変身コンパクト is. Turns out we have some lying around the house (ガシャポン souvenirs) 
And I had some trouble with the すいこ. At first I thought that すいこっていって was some kind of conjugation of a すいこる verb or something, but when they started discussing it, I realised that he was just saying that it’s called すいこ.
Again, I couldn’t find any dictionary entries and very little Google Image results. Maybe this is a local name for a plant that has a different common name…? It’s probably sorrel or some other type of dock (スイバ) because those are also included in the Google results and they are edible and sour (called ‘(veld)zuring’ in Dutch which has ‘sour’ in the name).
変身コンパクト 
Definitely the opening with the 夜の欠片 and 真っ黒な闇. An immediate sense of mystery and foreboding.
I also liked the kids’ conversation: discussing these outlandish things as if they are just an everyday reality is very kid-like.
She comes across to me as a strong-willed character, self-assured and like she knows how to get what she wants.