I honestly want to know what makes this game the failure that everyone claims it to be.
I don't know about anyone else, but I did not care for the gameplay. The biggest problems for me were the weapon mechanics and the pacing.
The guns are weak and the zombies rarely react to being shot, which makes the shooting boring and ineffective. If I could have upgraded my weapons, it might have helped make them more effective and allowed me to specialize in whichever guns I disliked least, but that's a feature RE6 does not have. If fact, with the exception of the occasional puzzle, combat is about the only feature RE6 has, which makes it even worse that the combat is so unsatisfying.
The pacing and the way the game handles the delivery of information is just ... very Japanese (in a bad way), poorly thought out, and up its own ass all at the same time. The best example I can give without spoiling much of anything is the start of Leon's campaign. I spent 10 - 15 minutes doing nothing but walking forward, during which time control was often briefly taken away from me so that the game can show me something trivial or that I'd have been forced to see anyway, because forward was my only option. In that way, the game seemed very intent on force feeding me every little sight, sound and emotion the developers wanted to convey ... and yet almost no actual plot information was passed on during this long, uneventful walk; it is time completely wasted and it was practically my first impression of the game. I spent as much of the game as I was able to stomach having a very tightly controlled experience painstakingly telegraphed to me, and it wasn't even a well crafted one. What's more important plot background is relegated to optional text documents found outside the campaign, which makes the rigid control of the narrative in the game even more of a joke because I couldn't understand the conclusions the game was so against letting me draw myself.
RE6 struck me as a game designed by people who will never be able to understand why their math equation for the perfect game resulted in something gamers don't like. --- "I can't buy a pack of smokes without running into 9 guys you've ****ed!"
Biggest complaints? - Lack of weapon upgrades - Action took front and center to engrossing and dark story line - Not much variation of weapons, certain weapons only available to certain players instead of being able to select what you want.
Still it is a fun game and doesn't deserve nearly the amount of flack it has received.