The book isn’t terrible. Foster does a creditable job of conveying the story of Star Wars. It isn’t great either. The plot of Star Wars is not particularly deep or clever. The book is good in that it shows just how the film adaptation made the story and characters work. The superb effects and the magnificent music combine to be more than the sum of their parts. Amusingly while reading the book the Star Wars music was on the radio.
The book differs from the movie with extra scenes including Luke meeting his friends and Biggs and Solo meeting Jabba, which would be included in the re-release of the Star Wars films in the late 1990s.
Interesting Foster went on to write a sequel that would be filmed as a low-budget film if Star Wars failed. Due to the success of the film an alternate, The Empire Strikes Back was made.
For anyone who is into Star Wars the book is worth reading. It’s quite entertaining and adds a few details and helps to show how good the films are. It also shows the weaknesses with the Star Wars universe that would go on to produce fairly poor prequels and the strange mess of the expanded universe. As a child I read the book and loved it, as an adult it’s a fun thing to come back to.