Primarily interesting is the fact that they claim that this is the most balanced multiplayer experience ever! My face would melt if this was true. They backed this up by taking out some perks that pissed a lot of people off - no One Man Army, no Last Stand (Final Stand is still in though), no Commando! It pissed me off that shotguns can't be used as secondary weapons, though. My primary load out in MW2 was an M4A1 and the SPAS-12.
Another would be the Support Strike Package. For players like me who can't get consecutive kills in MW2, this is sounding like a gift from Infinity Ward, Sledgehammer Games and Raven Software to those who suck. Getting 8 kills no matter how many deaths is much easier than getting 4 consecutive kills for me. I am slightly worried that this has the potential to be cheap and will be abused thoroughly. I am honestly hoping it is not game-breaking.
The third Strike Package would be the Specialist. Instead of air strikes and stuff you call in, you get more and more and more perks. It's like a legal hack! Ah, there is absolutely no way this could be taken advantage of </sarcasm>. I'm worried about this because the already good players are just going to be god-like. However, this might be something I could look into if I really want to get better at this game.
Weapon Proficiency is one more thing that has piqued my interest, but has also caused some concern for me. Basically, Weapon Proficiency is a way for you to level up your gun with extra perks for a particular weapon such as reducing kick and sway, adding two attachments, etc. In Black Ops and MW2, I found myself switching weapons every now and again when I get bored with a gun. In Black Ops, attachments and stuff were unlocked with a form of currency so rewards were almost instantaneous. With this new Proficiency mechanic, I think I'll have to stick with one gun so I can level it up a bit.
New game modes, MW3 has them! I wasn't very good at zombies, but this new Spec Ops game mode excites me because you get to use all 16 in-disc multiplayer maps! Team up with a buddy and let the good times roll! One more game type I think will be about as fun as a bag of kittens is Kill Confirmed. The objective of the game is to confirm the kill by picking up dog tags and to deny your enemy's kills by picking the dog tags of your fallen team mates. I think this is their way to minimize camping, because to get points, you'd have to run out and grab the tags. Then again, campers were never really known to be team players and would very likely not give a flying fuck about accomplishing the objective.
Kill Confirmed Kill Confirmed Kill Confirmed! That'll get annoying real quick.
In previous Call of Duty games, going prestige was nothing more than a way to show off how far you piss. This time around, there is a Prestige Shop, where an actual reward is present for taking the leap into a Prestige. That could very well change my mind about only doing it once in every game.
One of my greatest fear is a seemingly unbalanced rumored perk, the Assassin. It's supposed to keep you invisible from all UAVs and similar Strike Packages. We'll see how abused that perk will be when the game ships on November 8, 2011.