and definitely one of my favourites. A little late in realising that there was a novel, 21 years later, but I thought I would give it a try.
As would be expected it is heavily based on the screenplay, but it does divert, expand and add in a quite detailed plotline involving the alien artefacts.
To begin with the book practically mirrors the film including the dialogue, although it does start with an alternative scene on the surface of Mars. As would be expected of a book it is more detailed than anything a film could convey and Quaid's thoughts are much expanded upon and give a greater insight into the character whilst also explaining some of his onscreen behaviour. He is certainly deeper than Arnie portrayed him.
As the book progresses more detail is given of off screen events, such as what happens at Rekall post Quaid visit and who the man with the suitcase was, and sections added, such as a chapter on the shuttle journey between Earth and Mars when Quaid is in his fat woman disguise.
A major addition to the storyline is the previously mentioned alien artefacts and a whole chapter near the end is dedicated to expanding on what Quaid learns when Kuato scans his mind. There is no way that the detail in this chapter could have been in the film and I personally think that whilst it was interesting it was rather silly and is weaker than the screenplay. And why I rate it a 4.
Watching the film straight after the book certainly enhanced my enjoyment as I could add in the detail that was in it. It doesn't map across exactly, but what does are useful additions to the story.
For what this can now be got for, if like me you can never tire of watching the film, it can only add to what is already a masterpiece of science fiction film making.