A much-needed revolution to the Call of Duty series done right.
The bad: Can get boring after a while, no co-op campaign, only one map pack released as DLC
Let's put it this way: Call of Duty 4: Modern Warfare is groundbreaking. Not only does a successful transition to the modern setting from World War II stand out, but the way this game is made unlike its predecessors shows that Infinity Ward did what they needed to do.
First off, this game has phased out the older Ranked/Player Match system that Xbox Live used for the last couple installments. Now, you can play a Public game with a party full of your friends where leaderboard stats count, as well as a private game where you don't earn XP, stats aren't affected, and you just play for fun. This is a much better system than the days where you had to decide between playing for leaderboard stats or playing with your friends, and after a year and a half this system has practically replaced the old Ranked/Player Match system entirely.
The story puts you on two different fronts, the Marine Raiders fighting a fictional Opposing Force, and the S.A.S. battling a neo-Stalin Spetznaz army. The fighting ranges from the deck of a ship in troubled waters to the Middle East to the abandoned city of Prypiat to the inside of a missile silo. It is here you will find all 1000 of this game's gamerscore, as the game does its own method of achievements for multiplayer.
The multiplayer plays much like Call of Duty 3, where Y changes weapons, B crouches, and holding down LS sprints. But that's where the similarities end. Aside from a plethora of modern weaponry, ranging from claymores to AK-47s to P90s to Barrett .50-cal, each player is entitled to choose one each from three sets of perks which give the player a unique advantage. Examples include Stopping Power, which increases your bullet damage, to the ability to plant Claymores to even dropping a live grenade when you get killed. The level system is also totally new, in which a player can rank through 55 levels. Afterwards, they can stop or do it all over again up to 9 times to gain "prestige".
Game modes online include what you would have in Call of Duty 3, although this time Team Deatmatch kills are worth 10 points and you play until 750 or time runs out. Yes, you can actually decide whether or not to play Team Deathmatch or Free-for-all, unlike what the ranked match system in COD3 was like. A new elimination mode called Search and Destroy has been added as well, where one team tries to destroy a target or eliminate the opposition, while the other team tries to stop them. If these regulard game modes are too mainstream for you, there's new Hardcore variations to Team Deathmatch and Search, which provides a more serious and realistic experience.
Overall COD4 is an amazing package that should not be missed by any a FPS fan.