The book is famous. Most people know the plot (and even if you don't, most know De Gaulle wasn't assassinated), or have seen the film (or both), so the story isn't "Does he success?" It's more "How do they catch him?"
The writing is good too. You might think it'd be dated, but it doesn't feel that way (unlike early Robert Ludlum books say, which are dated). It can be precise in places, but it helps the stop rattle along, which is always a good thing for a thriller.