Innovation, bleeding edge graphics, in depth gameplay, realistic physics, a mature yet demanding community.
That's why this game sells 30 million copies.
I'm guessing GB give it 4 out of 5 stars... like they do with every other run of the mill shooter that happens to be popular.
Call of Duty stopped being innovative years ago, the community is mostly little kids and 30 year olds who are still little kids the gameplay is just look down sights and shoot. Selling a lot of copies doesn't mean anything past it's popular and if they give it four stars it will be because it's well made but they've played it six times already.