I'd have to agree with the Gamespot review.

User Rating: 7.2 | Call of Juarez PC
Overall, it's a fun game. I don't mind it being on rails as sometimes it's nice to be guided along the storyline. Environment raphics are great, sound is awesome (when both are working, see below).
Controls are adequate, although playing Billy and dodging everything can get boring. It's a western, EVERYONE should be gunfighting!

My biggest complaint is with performance. I have a new Maingear PC loaded to the gills, even an 8800GTX card. Playing in DX10 was good for the first few episodes and then it's like performance hit a brick wall, to the point of being unplayable. I even lowered the resolution and settings to "better performance" and it still ran horribly slow, and then looked bad too!
I updated my video driver and am in the process of updating my sound card (X-Fi Extreme Gamer) since the sounds were getting wonky too.
Hopefully that will correct things and I can continue playing, and actually the enjoying, the game itself.

Then again, it could be because I have Vista.