There is no balance, thats what kills the game.
You are given a host of perks, weapons, abilities, etc. that will almost never be used. They want the "Team Fortress" style of Gameplay, where different classes matter, but think that can be achived by letting everyone choose what they want freely.
Not only that, but some weapons are just broken. And Infinity Wards response is "lalalalalalala were not listening". The Killstreaks are broken as well; get a few kills and have access to a complete killing machine? The First Modern Warfare was nice; 3 for a UAV, 5 for an Airstrike, 7 for a Helicopter. The Helicopter wasnt too easy or hard to take down, and it didnt break the gameplay over its knee with a sickening "crunch".
If they worked on making the game more balanced, possibly removing the AC130 and attack helicopter (or make it so you need 20 kills to activate, and cancel out the Tac Nuke) the game would be a lot better.
Also. A Nuke. 25 kill insta-win. In CTF and Objective based. Fuck. That.