I have to agree with you on that point, Perdita. I can think of many cases when a book reviewer has given his or her "expert" comments after reading just the first few paragraphs and hasn't really grasped the plot. Terry's books are very popular in our local library and a group of readers like to post their comments for others to share.
Here are a few examples...
"Death's grand-daughter has to save Christmas with the help of a drunken god" - The Hogfather? Christmas?
"An apprentice sets out to build a perfect clock. It will kill time, literally and only the old Abbot of an ancient order can save the day" - Thief of Time.
"The wizards of the Discworld have invented cinematography and a lot of other problems" - Moving Pictures.

I'm going to start and pull these notes off the board next time I see one. :x