Of the four BSK books I read recently (for the purposes of recording a podcast), this one was by far the weakest. Even by the standards of chapter books for children, The Abominable Snowman Doesn't Roast Marshmallows has NO plot. The only thing that happens in the entire book is that the kids witness a very large man sitting by a campfire eating Mega-Marshmallows in the middle of a snowstorm. They jump wildly to conclusions in a way that, for the first time, I found straight-up annoying--there was something kind of charming about their wide-eyed wonder in previous books, but here they just invent wholesale the idea that if they don't chase the Snowman away, winter will never end in Bailey City. It's like a bad episode of Rugrats. Then it ends with a sled chase down a mountain that feels like the literary equivalent of the cringe-worthy slapstick you'd get in a Disney Channel Original Movie. The book has WAY more illustrations than the earlier books in the series, depicting moments in the story that don't remotely NEED to be illustrated, so it feels like a ploy to pad out the page count.
I guess I can't blame the authors too much, since they'd been reworking the same formula at this point for fifty books over the course of fourteen years. Still, for the penultimate book in a beloved series, you'd hope for something a bit more energized.