This 20th Anniversary Edition is a remake of Gabriel Knight: Sins of the Fathers. It features new HD graphics, new puzzles, new voice acting, a remastered soundtrack by the original composer, and even some new locations. The game stays true to the original in terms of the story, and while it is still a 3rd-person point-and-click adventure game, it uses 3D graphics and character models instead of 2D graphics with sprites.
Unlike the original, the game includes a hint book which lets you gradually (tip by tip until the actual solution) view tips on how to solve puzzles. There is a certain waiting time between checking the next available hint. Also, the hint book is integrated as Gabriel's diary where he keeps track of the story and his ideas which may provide clues to solving some puzzles or figuring what to do next. And finally, the book also contains extras which are tied to your current location. The extras include artwork comparison between original and remake graphics, sketches and storyboards, and commentaries from the original game designer, namely, Jane Jensen.
Pre-ordered GOG release also included full digital soundtrack.