its pretty good imo, one of the best ever, the starting mission was just great that set things off, it encourages the players to continue playing cause there is lots of action in upcoming missions
my fav mission is where we play as captain price. where he was on a mission years ago. that mission was the best in the entire game, it had stealth, action and gunplay was pretty good too
the plot of cod 4 was pretty easy to follow too