Thing is, Giacchino only had four weeks to composer a full blown score to a Star Wars film. Not an easy task for anyone. Giacchino was up to the task and crafted a score that not only provides brand new themes for the characters and situations in the film, but also references themes and style from John Williams score for Star Wars: A New Hope. And we aren't talking about the more famous thematic moments here, we are talking about the less known motifs, such the one used for the Death Star and one used for Stormtroopers and Darth Vader before Williams crafted the well known imperial march for The Empire Strikes Back.
All told Giacchino's score works very well in the film and for all his references to the older scores, I enjoy his new material a lot. His theme for the fearless Jyn Erso may be the best of the new material. Here is a suite version of her theme followed by his Hope theme, which makes a good solid nod to William's main Star Wars theme. Enjoy.