Call of Duty 4 Modern Warfare

Released in April 27, 2007, Call of Duty 4 changed everyone's perspective on the Call of Duty games.  The Call of Duty games before CoD4 were set in World War 2.  When Infinity Ward (game developer) switched to modern times, they started a whole new line of games to come.  In my opinion CoD4 is the best of the Call of Duty series for online multiplayer.  The perks were well grouped together and well thought out.  You had to make sacrifices to get other abilities.  Such as, in order to use UAV jammer (which makes you invisible on the mini map during a UAV) you can't use stopping power (guns do more damage to enemies).  Another example is, if you want to use the grip or grenade launcher on a weapon, it disables the first perk slot. This made the game more strategic.  Also, the maps were simple and allowed  good overlooks for sniping while still providing close range combat.