I understand your point. I can't say that I agree with it totally, but I understand it.
That's how I see it:
Rennes-le-Chateau was extremely detailed as a set for Gabriel's new adventure, no less than New Orleans or Monaco. Moreover, it was extremely adherent to its real-life appearance: the geography of the area was well represented and carefully depicted, as were the inherent geometries of the valley itself, not to mention the architectonic details of buildings such as St. Magdalene Church. Furthermore, the historic and religious background of the region was lavishly polished: from the Roman domination to the Merovingian Kings during the Middle Age, from the Knights Templar and the Cathars around the '200 to the discovery of Abbot Sauniére, the history of Southern France, and Rennes in particular, was precisely addressed in the game, with an amount of detail unknown to Dan Brown or to other games (I'm thinking of Broken Sword 1, even if I only played it half-way), whose takes on these subjects - the Templars, mainly - feel shallow and pretty inconsistent, in comparison.
The character were indeed less developed than the ones seen in the first two games, particularly Montreaux, who can't really stand the match with Von Glower or Malia Gedde. Anyway, the treasure hunters were amusing and well rounded-up, in my opinion: some of them lacked the charisma of some of the characters from the previous games, but some of them - Baza and Wilkes, mainly - were believable and very well written.
I have said that The Beast Within
story is unbeatable, and I really think it. But Jane Jensen in all the three chapters crafted powerful and magnificent stories, and it's only a matter of tastes in preferring one or another. GK2 has a deep, meaningful story of self-discovery and a plot worthy of the best Bildungsroman ever written, but - nonetheless - GK3 has a thought-provoking plot that deals, with class and elegance, with profound religious and philosophical themes, showing a courage that was ahead of its time.
These are the reasons for which I'm also crazy about the third game...
... Anf, anf: one day, I'll also tell you why I'm crazy with the first one, since I've done this for the latter two