Grim Fandango is hands down the best adventure PC game to be created.
The story puts you in the shoes of Manny Calavera, who is a Grim Reaper and a travel agent, who is sent to the Land of the Dead to work off his time and be able to rest. Manny enjoys his job, hoping that his job comes to a finish any minute, but turns out not to be that way. Manny stumbles into a web of corruption within his department and goes on a journey to bring down an evil empire.
The script is very well done and has it's own movie nods into it also. It has its betrayls, plot twists and it's cast of interesting characters. The art style of the game is very interesting, which is what separates this from other adventure games.
Puzzle solving is a major part of this game and will make you think instead of doing something simple. Some puzzles require a lot of attention and patience to complete, but there all fun to do.
In the end, Grim Fandango is one of the best games ever made and also my personal favorite so far. So, if you haven't played this yet, go out there and find a copy and play it. I just hope a sequel can be made soon.