Gabriel Knight: The Beast Within is clearly miles ahead of its predecessor. I hadn't read this one that much (twice, at most, really), and I didn't remember much of it except for the general story of the game. I didn't recall it being SO good and entising.
One of the best things in the book is how the story is told from two points of view: Gabriel's and Grace's. They're both working on the same case, but start off at different backgrounds, so that makes them both important characters, and the "hero" and "sidekick" idea is not that obvious. Grace is Gabriel's assistant, but she gets a lot of the action, too (in her own way, of course, she's more the intellectual and historical side of the story). We also get to learn a lot of more of the relationship between them both, even if they are appart, and a bit of their fears and doubts about themselves.
And Jane Jensen took the story to another level. While the idea of the game and a lot of its situations are still included, they're explained from a different point view and a more realistic, less round-about one. And I think it's absolutely amazing how this story of (supposed) fiction revolves around real history around King Ludwig II of Bavaria. I've researched a bit and it's like everything coincides: he was diagnosed and condemned as insane and the real reasons of his death remain a mistery. That's where the author seizes the opportunity to come up with a fantastic explanation, but the rest of the subjects touched upon his history seem to be REAL.
It's a much darker story as Sins of the Fathers, and it deals with a lot of duality for the main characters (hence, the title, I guess) and scenarios that trully put the heroes to the test. It's unexpectedly good.