Why do you ask why people are hyped for MW3?
It is one of the most popular online FPS games (I personally never enjoyed it)
It is one of the best console FPSs (I prefer Quake Live and Counter Strike on PC)
It has decent graphics and solid gameplay (You get what you pay for)
Just accept it for what it is. I know why you are angry! Games like NieR or the World Ends With You get no hype while a new Call of Duty is the coming of Christ apparently, even though its just a revised version of the old one, but we can't hate on it since it is... What it should be I guess.
How should they innovate it in your opinion? What should they change?
The truth is , they can only change the setting and graphics.
Some gamers like competition, some gamers like FPS and some gamers like 'realistic' warfare settings.
I just think that gamers that started in the 90s are less competitive (meaning they curse less and try to become better rather than curse others out, not that they don't enjoy competition).
Gaming is like reading books, I think. If you started reading early on, you have most likely read colorful stories at the age of 6-10 and as you get older you started enjoying more complex stories. If only the Gamers that started playing as they grew up existed right now, Call of Duty most likely wouldn't be hyped so badly now or might not even exist anymore or be completely different.
Just like every other type of media though, gaming needed to become more mainstream. Nobody could take stories in video games seriously if they hadn't grown up with them, just like people can't read Shakespeare and appreciate his work if they have never read a book before, so they had to bring in more and more competitive gameplay that everyone can enjoy right away with less focus on the story, kind of like the Twilight series that just tries to concentrate on one topic and make it less complicated than one of the more refined love stories.
Voila, Call of Duty. Be grateful for it, because developers wouldn't have the money to make the Mass Effects and Skyrims without the millions of new players that were introduced to the Gaming scene. If you don't like it, don't play it, but appreciate what it has made possible.