I remember playing this game TOO much when I was a kid. My cousin, who was older than me, showed it to me just when I got the xbox 360 and I have never been so happy with another game. There were hundreds of times I would only play it for one specific mission (the jail) and then complete the whole campaign again. Sadly it can't be played officially on pc (ehem, steam), but I would love to play this experience again.
The mechanics of playing dead to decrease the aggressiveness of your enemy or carrying your partner when he was wounded (often your friend when playing in coop) were the most fun. The weapons felt great and the boss battles were enjoyable.
It felt very special to play it with someone else, but even playing it alone you could feel like you had a friend nearby (be it Salem or Rios) thanks to the dialogues or gestures like playing rock paper scissors before starting a shootout... this game is very special.