All three books are similar in format and style, covering Guy's stays in the titular cities. His brand of self-deprecating humour ensures that the often-stark, strange environments, which are so different to the Western world, are viewed with friendly curiosity and bewilderment.
The main benefit of the graphic novel format is its visual nature: as the old saying goes, a picture paints a thousand words. Jerusalem brought back many wonderful memories for me, and although I've never been to North Korea or China, in some small way I feel I now have. I'd wager that there is as much information in Delisle's 175 pages or so of drawings as there would be in as many pages of solid text, albeit the latter would be considerably less amusing. Pyongyang in particular could have been a thoroughly depressing book, but instead it is quite oddly affectionate (and never less than thoroughly fascinating).
My only sadness is that I have just one of Delisle's books remaining - Burma - but I suppose all good things must come to an end. Here's hoping that his travels will continue!