Here are my opinions:
1: The maps. Many of you would say lag as being the biggest problem but for me it's the maps. They are all too similar, and all too small.
I regularly find myself being shot in the back, and being spawn camped. Every time I fire my gun, I know that there is someone nearby looking at the little orange dot on the radar and that I'm going to die while I'm reloading. I have hardly used a sniper rifle because there are no suitable maps to use it on! Previous CoD games had a good variety of maps. Some good, some not so good. But they catered to all types of player. I personally liked the bigger maps like Fuel & Wasteland, and tried to avoid maps like Scrapyard and Rust because of the simple mindless gameplay they inspired. The poor maps in MW3 are the reason why I'm not playing until some new (or old) maps arrive.
2: Lag. There has always been a bit of lag in CoD games, but it was generally acceptable in CoD4. W@W, & MW2. Much has been said about it in other posts so I won't dwell on it here. Black Ops was when it got much worse, and it's still bad in MW3. I've heard that it's because data is being sent to Elite. Is this true? If so, this is the end of CoD because Elite is here to stay.
3: Boosters / Cheaters. Boosting was a huge problem in MW2 that Infinity Ward never bothered to address. It was left to us gamers to hunt these idiots down and ruin their game. Boosting disrespects everyone else playing the game. In my opinion they should be permanantly banned from all CoD games. I have also never understood why people would want play the game in the most boring way possible. I mean, MW2 had so much variety in how to play the game. More than any other CoD title. And all people want to do is take turns shooting each other in the head. How much fun can that possibly be? You can get all the titles, camos, etc. by just playing the game and having fun while doing it. The mentality of some people is just bizarre. Games are fun and are supposed to be enjoyed to the max. Treyarch, to their credit tried to do something about it in Black Ops by adding the 'report' option, and by banning the Tactical Insertion in certain game modes. It didn't totally stamp it out, but cut it right down to the point where I hardly ever saw any boosters. So what do Infinity Ward and Sledgehammer do? They bring back the Tactical Insertion for all game modes? Why? What did you think was going to happen? I've already seen several games of MW3 with boosters, and despite the fact I've reported them, they have not been punished. And they've even given them a new game mode so that they can rank up quicker (Kill Confirmed) by collecting their own tags. And nothing is being done there either.
4: Quickscopers / Dropshotters. This was a major problem with MW2. People abusing the auto-aim feature to get cheap kills, and people using modded controllers to drop to the ground quickly. Again, Treyarch stamped these out in Black Ops, and again clueless Infinity Ward & Sledgehammer allow these nooby tactics to return in MW3. In MW2 I would deal with these idiots by noob-tubing them. I know noob tubing is generally frowned upon, but the way I see it is: if you ruin my game by quickscoping, I'll ruin yours by tubing you! So Infinity Ward & Sledgehammer nerf the grenade launchers in MW3 to the point where it just isn't worth using them. My main issue with quickscoping was that too many people were doing it. Too many people all using the exact same weapon and set up. Too many games where all you can hear is the same gun noise over and over again. Boring! So many weapons available, and you only want to use the Intervention. And as for dropshotters, there is nothing skillful about pressing a button on a modded controller!
To summarise, I am very disappointed in MW3 and cannot see much improvement coming to this and future CoD games. The fact that it is too similar to MW2 was never an issue for me as I liked MW2. But Infinity Ward have not made any improvements and have taken out much of the variety that MW2 had. The magic is gone from CoD. I hope you are reading this Robert Bowling. This game has further damaged Infinity Ward's reputation that was already damaged when they didn't fix the hacking on previous games!
All I want are 2 things:
CoD4 to be fixed to stop hackers.
MW2 to be fixed to stop hackers.
Then I'll never have any need to play MW3 again because this game is screwed!