Good and Bad
I enjoyed the campaign and recommend everyone play it. It was immersive, fun, and a great way to introduce new weapons presented in the multiplayer (I like to play the campaigns first before the multiplayer because there are usually connections between the campaign and the multiplayer).
My mixed feelings of the game are in the multiplayer. I'm not a pro multiplayer gamer, but I'm not totally horrible and can hold my own if I'm on a team. One of my issues is the inconsistency of kills. I don't care about the ratio, but I have matches where I only come out with 2 kills. In Call of Duty games prior to Modern Warfare 3, I normally averaged approximately 12-15 kills, with about 1:1 ratio which is why I don't normally care about the ratio. After 20 hours of multiplayer gameplay, I feel I should be better, but I'm just about the same as when I first opened the game, and I know it's not because of the user.
Another issue I have is when I have my cross hairs, iron sight, red dot, etc. on an enemy, I expect to get at least hit markers. In many instances, I don't get anything (it happened at least 10 times today in about an hour span). I don't know if that's anything to do with the gun sway they have incorporated into the game, but if this were to happen on a real battlefield, they guy in front of me wouldn't have gone home unscathed. This happens so often that it make the game not fun anymore (I play for entertainment value, not professionalism).
Another small issue I have with the multiplayer is that the maps seem a lot smaller than maps in past Call of Duty games. I'm not saying that the maps have to be humongous like in Battlefield, but the maps could be a little (notice I said a little) bigger. The reason why is I feel like whenever I spawn, there is always an enemy closing in that wasn't there during the kill cam, or each corner I turn, there is another enemy already in the process of killing me. This is where bigger maps could help.
One more thing I dislike are the gun stats. The pistols are a joke. How can a .45mm have the same stats as .9mm? None of them are worth using. The machine pistols have made a comeback from Modern Warfare 2, and are still a lot of fun to use. The Launchers are still fun to use to blow up enemies, helicopters, etc. What I don't understand is how all the automatic weapons all react the same way. I swear I try using different automatic weapons and I still come out with the same result.
One thing I like about the multiplayer is the new game of Kill Confirmed. What a genius way to enhance Team Deathmatch. I've always liked a good match of Team Deathmatch, but you can use the dropped dog tags as bait for enemies trying to snatch them.
Another thing I like is the comeback of the option of changing the Titles and Emblems of your gamertag. I wish Treyarc would introduce this into their games, and I missed that in Black Ops. I'm glad that's back, and the Infinity Ward's sense of humor within the titles are fun.
Now that Modern Warfare 3 has been out for a while, it is worth the used price. It was a pretty hyped up game, but it didn't have the luster that past Call of Duty games have had. The campaign was great and a lot of fun to play. The multiplayer needs a lot of work for the next installment.