Best adventure game ever. period.
So, this is the setting... Good stuff isn't it? This is where it gets better...
The character in this series is one of the most well developed I have ever been able to play in my whole gaming experience. Gabriel Knight is a clever mouthed, good looking womanizer with a pronounced Louisiana accent that doesn't care too about doing things by the book. By the end of the game, you will feel attached to Gabriel, almost as though he was somebody you know...
Also, the way the story is setup gets you wanting more, all the time. This is a classic detective story, where you need to use your head to solve puzzles which are always directly linked to the story. No gratuitous difficulties here, no stupid situations where you need to craft up new items based on complex item combinations.
The dialogs are also a big part of the overall enjoyment of this game. Great acting, first of all, and second of all, the conversation system will let you ask questions, discover new facts, and add new options of conversation latter on. You might discover something about a famous Voodoo priestess, but need to know more detail in order to advance in your quest. So, from that moment on, you will be able to ask that question to other characters in the game, meaning you will revisit a lot of the locations and talk to the same people again and again. But hey, this is great here, because you are gathering more and more information, and the relationship between Gabriel and the other characters will evolve as time goes by and the more they know each other.
OK, I could go on and on about this game, but I'll stop right here. Bottom line is, this is the greatest adventure game to date, in my humble opinion. This game really sticks on you. It's been about 10 years since I played it and I still have very found memories about it (which were renewed since I got another shot at it 2 years ago!).