<spoiler=Modern Warfare 3> Yeah, shocking, I know, a sequel to a game I thoroughly enjoyed.
Except this would be much, much more focused on the single player.
The game would start with Soap recovering from his stab wound in an Australian safehouse, with Nikolai, Price, and an Aussie Task Force member who survived the
Jedi Purge betrayal by Shepherd, who I have yet to name, and the America/Russia war is still going furiosly, with America having the upper hand at the time.
There would be two contrasts, in one half of the campaign you would play as Soap, who, after having all he thought worth living for lost and ruined by Shepherd and his lack of care for humankind, has become a revenge crazed killer, hell bent on finishing the job. Which leads to another thing, Shepherd survives.
If you think he died at the end of MW2, you're stupid. Sorry, but he got stabbed in the eye. There was no way in hell it penetrated through to the brain, and even then it probably wouldn't have killed him. Soap was severely wounded, and was throwing a knife from lying down. Sure, it would've fucked up Shepherd's eye, but killing him is a far less unlikely outcome than simply losing the ability to see in one eye. And if the arguement about him dying of blood loss in the desert comes in; Nikolai found two guys in a sandstorm on his own in a Little Bird. The entire Shadow Company can sure as hell find their bloody leader in the same conditions.
So anyway, Ramirez and co return, and the gameplay is real Call of Duty; explosions, gunfire, war, war, and more war. Epic fights rage across Russia as you smake your way to Moscow, thundering through Russian defenses as you go.
However Soap and co's story is far different. A much more personal vendetta, the gameplay is much more stealthy and the most common guns you'll use are pistols (Which have been bulked up noise-wise for this, as most games have quiet pistols, these feel like actual weapons of death rather than just a last resort sidearm. There are also much much more varieties to use.), and there will be much more open missions as the locations are mostly populated cities, such as the starting location of Melbourne, Australia, going to Venice and London later on. You may be presented with situations where Soap gets the choice to kill witness civilians.
Halfway through Ramirez and co get recruited into Shadow Company, and the missions revert from the wartorn battlefields of Russia, to the Special Ops missions of the classic Modern Warfare. Take out Task Force survivors, and do general spec ops shit.
So anyway, I haven't thought of the giant middle part at all, but the ending would be going back to Chernobyl where Shepherd, finding out his life is threatened by one pissed off Scotsman, is in hiding with a bunch of Shadow Company troops, including our favorite Do Everything! guy and his buds.
After an epic mission, during which the Aussie dies (Nikolai will have perished by this point.), a standoff occurs, with Price and Soap holding guns at the Americans, and Shepherd, Dunn and Ramirez (Foley dies also by now

) doing the same to then. Then Makarov shows up and holds two guns to both Price and Soap, and Shepherd and him have a little talk about their cooperation. He then does a breif speech about his own loyalties, stating he is loyal to noone, and letting in a secret that Price hired him to be a double agent for them against Shepherd, which allowed them to find him Chernobyl. But Makarov still has a grudge against Price, and he switches the gun aimed at Soap to Shepherd, and shoots him point blank in the head, and shoots Price too, but hitting his chest. Dying, Price tackles him out of a window, and Soap, dumbfounded, is detained by Shadow Company and arrested.
Not the happy ending you expected, eh?
But there's more! If you complete every mission on Veteran, along with all Spec Ops missions at maximum stars, and also reach highest level on Multiplayer with every gun attachment unlocked, a secret final mission is unveiled.
In it, you play as Soap in jail, and you walk around your cell until a guard walks by just a little too close to your bars.
Not wasting a second, Soap grabs his steals his M9 pistol, shoots him, and steals his keys to release himself, before taking his Vector too and runs, trying to get out of the building.
This is easy, since he was actually being held in a low security prison before being moved to a much higher security prison.
Shooting your way out, you eventually reach the front gate, where a van parks, opens its back doors and a fimiliar face reaches out to pull you.
It's Gaz.
Yeah, I know he seemed to have got shot in the head, but I'm stretching it a little, from the angle Soap was at it sure
looked like he got shot in the head, but in this version he was shot in the chest, and survives, except running from the SAS for reasons left unknown.
And now here he is, busting his old squaddie out of the nick.
He welcomes you with a "Good to see you again, mate." Before closing the doors as you drive away.
Yeah, I kind of got a LITTLE carried away. Apolagies for the wall of text.
[/spoiler]
I would play that game. I would play the fuck out of it.