Gabriel Knight 2 was the first full-motion video game I ever played on my brand spanking new PC back in 1996. I think I even got it as a birthday present. It was also the first game to carry a 15 sticker on it, and to be honest for at least one scene in the game.
Gabriel Knight was very much in tune with the X-Files generation. You were descended from the Ritter family, German nobility who functioned as Schattenjaegers, Shadow Hunters. After investigating a voodoo cult, discovering your heritage and avoiding dying in the first game the second game saw you investigating werewolves in Germany, despite your character couldn't speak German:-
The intros were awesome:-
The Beast Within Intro
You also had a female sidekick who did all the legwork, called Grace. Obviously there was sexual tension between the two of them (damn 3rd game cliffhanger!):-
It also saw you in search of Wagner's Lost Opera, and even includes a pretty darn cool opera scene:-
Gabriel Knight 3 I wasn't so fond of. There didn't seem to be many memorable confrontations (the hunt for the werewolf in GK2 has to be played to be believed) and it got a bit Da Vinci Code for my liking (long before that was a gleam in Dan Brown's eye I should add). And as usual Gabriel Knight 3 was the only one of the games to end on a cliffhanger. Naturally no Gabriel Knight 4 is forthcoming from Sierra.