I missed out on this gem growing up which is a shame. I would have adored this book as a kid. I was quite entertained as an adult reading about the treasure hunt/murder mystery the sixteen "heirs" embark on.
The characters were a delight. My personal favourites were the secretary Sydelle Pulaski, Turtle and Doug Hoo.
Sydelle's theory that a twin was involved is quite realistic due to the never ending twin plots in books or Theo's chess idea.
Raskin effortlessly skipped from character to character and each voice was different.