The explanation of punctuation was most impressive to me. When I was a junior high school student a teacher said that punctuation was one of the most difficult things in Japanease. It is very difficult to determine where to locate comma or period. I usually write them almost automatically. But once someone asked me why, I would not answer on a logical basis. So I was excited about their description.
I was shocked to find forgetting some paradigms of irregular verbs. I would like to consult my dictionaries to remenber them.