Play it. Top-tier game, man. What's so great about it? Other than it being one of the most quotable games ever, it's just damn fun and a joy experiencing. Here are some highlights:
The entire Mexican Day of the Dead atmosphere throughout the whole game. You cannot find a better realized world.
"Manuel, are you... in love with her?"
"Love? Love is for the living, Sal."
The balloon animals.
"Run pigeons, it's Robert Frost."
Finding out just how far down the totem pole Manny is at the DoD.
"MANNNNNYYYYY...!!!!!" and Glottis in general.
"Viva le Revolucion!"
The Land of the Living.
"Good, because our ride wasn't ostentatious enough."
"This world is for suckers!"
So much more.
Load this up, IMMEDIATELY patch it, then have fun.