The game that started the Wild West craze (I'll just ignore Red Dead Revolver since it had 0 depth compared to CoJ), and one that put Poland on the big-boys-in-game-development list (with Techland releasing CoJ and CD Projekt RED releasing The Witcher in the same year - now-distant 2007), Call of Juarez was a marvel at the time: with raving reviews praising the tech, the vast (but pretty empty) locales that gave you a sense of freedom, and with Wild West theme that was rarer than a horseshoed unicorn, it won the hearts of many gamers world-wide.
Having played it recently 'til completion, I can say that it withstood the test of time and is perfectly playable on new systems, offering some 10+ hours of shootin' and sneakin'. The story is nice, although not better than in it's sequel/prequel Bound in Blood (which btw ties the McCall saga in a bundle perfectly), and the music is okay. Be sure to play it on Hard, unless you want a quick & safe ride through the game.