As fantastic as the single player campaign is, taking Call of Duty 4 online is the real highlight. In an age where online shooters are a dime a dozen, Call of Duty 4: Modern Warfare stands out from the pack with a unique system of “perks.”
A “perk” is basically a special ability, of which you’re allowed to have three at any given time. These can do a wide variety of things such as make you stronger, make your bullets do more damage, allow you to reload faster, give you the ability to detect mines, etc. Some of them are really creative, such as Martyrdom, which allows you to drop a live grenade when you die; another interesting one is Last Stand, which keeps you alive for a little while after you “die,” propped up on one elbow and firing your pistol.
All of this on top of already solid gameplay and a lot of fun modes make playing Call of Duty 4 online insanely popular.