Not as good as Tarantino says but undeniably pretty good. The book is odd because Minahan indulges himself by going into a lot of extraneous information about the protagonist before getting to the inciting incident which occurs at the precise midpoint of the novel. Perhaps he perceived that there wasn't quite a full book here so he had to delay the start of the action. Tarantino's idea is surely that that 'filler' material is quite good, and that's right.
The final act is riddled with implausibilities which merely signal that this is indeed a novelization and not a proper novel. Having said that, the final account of the nonsense is well handled.