Whereas I think the previous volume extended the "drama" a bit too much, I think this one got the right balance. Loads of character building, great story and an incredible finale of the volume.
In terms of language learning rating, I have to rate this one as the highest I've read in the series so far. The language used is very natural and I found it much easier to follow than in previous volumes.
You'll like it, if you liked Goosebumps
Entertainment wise, I think this is a decent one. Like with most Goosebumps books, not much really happens for most of the book, but think this book does a better job than others in the series, perhaps because ventriloquist dummies are creepy on their own.
Language level wise, I think this is close in difficulty to the Zenitendo series, this being slightly easier.
Personally, I find Goosebumps books great for extensive reading practice. They'll repeat the same vocabulary and grammar patterns