Pros: Game play, graphics.
Cons: Short, but very intense. No cooperative multiplayer.
The bottom line: Lots of fun. Maybe too much for some people. I've played it twice, and will keep it to play again.
The first three Call of Duty games were set in World War II. As the title implies, Call of Duty 4 is set roughly now. The player takes the roll of two special forces operators, a British Special Air Service commando, and an American Force Reconnaissance Marine. As you may know, British SAS are the United Kingdom’s equivalent of US Delta Force. The SAS commando character storms a ship at sea, provides sniper support to an infantry assault, raids Russian enemy camps, and even retakes a nuclear missile silo. There is also a flashback scene with a realistic sniper mission, meaning that most of the level involves trying to sneak into enemy territory undetected, assassinate a terrorist leader, and the escape an overwhelming enemy force. There is also a round where the player takes the role of a gunner on an AC-130 gunship. The AC-130 Spectre/Spooky is a military transport plane equipped with cannons, miniguns, and a 105mm howitzer artillery piece flown by US Air Force to provide close air support and strike capability. Covering an escape and extraction through the inferred cameras of the gunship is unique, it wouldn’t be fun if it was the whole game, but the short segment is just perfect.

Force Reconnaissance are an elite component of Marine Expeditionary Units (Special Operations Capable) [MEU (SOC)], which is itself an elite type of unit within the already elite US Marine Corps. A MEU (SOC), is a self-contained fighting force comprised of infantry, light armor, artillery, and aviation (helicopter and Harrier) components. In this game, the Recon Marine character supports a heavy armor element (specifically an M1A1 Abrams Tank), and a helicopter assault force (including a phase where your character mans the Mk19 automatic grenade launcher on the door of a Blackhawk helicopter).

The games realism begins with the weapons and equipment available to the player. You start with some of the most advanced weapons we know about that are available to western soldiers (although, I don’t know whether the British SAS use of American rifles is realistic), and can pick up a variety of captured enemy weapons (often the ubiquitous AK47) along the way.

The next realistic element is the plot changes, in which mission objectives suddenly change, when intelligence proves wrong, or things don’t go according to plan. For example, an assault becomes an evacuation, which then become a rescue mission when a helicopter gunship is shot down.

The combat can actually be frightening at time. You face a very savvy enemy that will flank, ambush, use snipers, explosives, etc. Your help is an equally smart team of Commandos and Marines that, unlike many games, don’t leave most of the work to you, but fight as well as you, and sometimes better. There are also the occasional help from air support, that sometimes makes all the difference. The result is that you have to fight at the pace of your support, running too far ahead isn’t possible, because you’ll be killed quickly by your self.

The combat system is excellent. There is an opening tutorial to get you used to it, and even to evaluate your skill so you can set the games difficulty appropriately. I found this game to be challenging. I agree that the single player game could probably be done in a full day of playing, but I got killed frequently enough that it took me longer.

The graphics are very good, very realistic. The story isn’t anything special, but it moves the action along, and you pretty much always know why you are doing whatever it is you’re supposed to do,

This game is very intense. There is, obviously, violence, and it’s pretty graphic at times. From time to time, you also encounter dogs, that will pounce on you and go for your throat, unless you can break its neck. This is not be suitable for young children. However, there is a clear sense that you are the good guy. Honestly, the games message is a grown up one: soldiers fight and kill to save others, and in this case, the guys we are fighting (Russian and Mid Eastern extremists looking to overthrow their respective government, and willing to use nuclear weapons against either the US military or US civilians) are bad guys.