Personally (having played all of them) i find this as the best by far, i also enjoyed Call of Duty 2, but i thought what 2 lacked, 4 made up for. To this day i'm not even sure about what it is that i liked about that game, i think it was just the simplicity combined with great maps and great guns. The game has gone downhill since Call of Duty 4 in my view and i can't ever see it coming back to how it was.
Now that the game is becoming evermore deserted i have started playing Counter Strike: Source every now and then and i'm really starting to enjoy it. If you know any other games similar to the style of these ones if you understand the style i'm looking for i would appreciate feedback.