I will be honest, I have not touched the Multiplayer yet. However, I wanted to at least counter some of the campaign complaints. Typically, I hit Multiplayer first and then eventually play through the campaign....sometimes.
The campaign is exceptional. The characters are maybe the best CoD has ever seen. The story is engaging and remains interesting throughout. The game does take a hard look at modern war and leaves you to form your own opinions (which it seems like many people must struggle with as it seems to be an issue for some). There is a particular line from Price in a car scene that I won't spoil, but it is probably my favorite line in the game.
The campain is short. About normal for CoD but maybe slightly shorter than normal. That said, if you have played CoD in the past, you shouldn't be expecting a sprawling campaign. You should be expecting varied missions with great combat. I finished the campaign in < 8 hours for sure, but not exactly sure on the time (played several hours two different evenings).
The AI can be dumb in some cases. The difficulty sometimes relys a little too much on dialed up accuracy and liberal use of grenads. During the several stealth missions, you will also notice the enemies not respond to things like lights being shot out, bodies under their feet, etc. And even during non stealth missions, if you stay mostly hidden, and flank enemies, they are almost always completely oblvious to you existing.
However, even with the dumb AI, I can say this is maybe the first CoD campaign ever that I have thought about replaying.
Side note, there is a bonus scene after the credits that is worth watching if you are familar with the previous MW games.