The main things I didn't like about this book were 1.) Bobby is regressing in his speech. Again. And 2.), the mystery in this one seems to be put on the back burner. For 1.), Bobby seems to be going back to more of the way he was in the earlier books. Upon opening a Trixie, I never seem to know what Bobby is going to be like. In some like Phantom Grasshopper or Uninvited Guest, he is surprisingly mature for his age. In this book though, he seemed to be back to his 4 or 5 year old self. One example is when he repeats himself and says things like "Trixie doesn't always do her best, and Mart doesn't always do his best, and Brian doesn't always do his best..." etc. My sister is around Bobby's age (7) and she never did anything like that that I can remember.
For 2.), I think that the mystery is not really the primary focus in this book. We don't get into the mystery until near the middle of the book. Up until then, we've learned some boring things about old cars, and spent some time talking to a mysterious stranger. But there's no real mystery. Then, even after the man has been hit, Trixie's on the case, but not as curious or persistent as she is in most of the books. There is a lot of time taken out of the book with the girls collecting donations, but it takes a lot of unnecessary time out of the book that could have been used on more things related to the mystery.
Overall, this is a good book. I liked the ending, and the Bobwhites are pretty in character. No major slipups like Regan being the Wheeler's chauffeur as far as I can remember. It's not in my top 10, but I still enjoy it.