The biggest problem is that people confuse quality with context. Call of Duty, for example, was praised highly around the first Modern Warfare game because it did something different and innovative. It then continued to evolve and iterate about as quickly as beloved games like Mass Effect of Half Life, but it got attacked for being stagnant and cliche. This is because of the constant slew of games that tried to be Modern Warfare clones. If Modern Warfare were to disappear for 15 years, and re-emerge in a world where all shooters are Serious Sam style cheese fests, Modern Warfare would be put on a pedestal by, "Core" gamers as a savior of creativity and good design. People attacking popular shooters arn't really angry at the game itself. They are angry the stagnation of the medium at large. And honestly, lack of variety is the source of most video game criticisms. A scantily clad piece of feminine eye candy isn't bad, its that every female in video games are like that. good graphics arn't bad, its bad that everyone seems to feel like they are priority 1. Regenerating health isn't bad, the lack of games that truly benefit from a style of play that benefits from health packs is bad. And so on.
Oh, also, some innovations by popular games are innovative and cause popularity by changing the game away from what some gamers expect. Call of Duty introduces elements of randomness and a focus on kill streaks that don't match shooter expectations. It's not bad, but it does confuse old players while drawing in new ones. Old gamers basically try Call of Duty's pancakes and say, "This is horrible French Toast!" Well of course it is, it's not french toast.