is that he made/makes foreign travel easy to understand and comfortable for so many people who don't have extensive travel experience. Having never been out of the US (other than Canada) before that trip his guide to Italy was a huge help in planning everything - all in a single easily carryable book.
IMO he makes travel not scary for people who dont have extensive travel experience.
Since that first trip to Italy we've been to roughly 40 other countries but have on occasion bought his guides for easy to digest insights into different places. He has introduced hundreds of thousands - probably more - to the magic of Europe in a folksy, comfortable way. I like him.