I'm NOT an RE super-fan -- the avatar is because I like the "tits" joke in Revelations -- but I am a fan of action games (Vanquish, Bulletstorm and Kid Icarus Uprising being my favorites).
If several demo sessions are any indication, RE6 is mechanically sound in terms of basic movement, camera functionality (once dialed down), inventory management, and running and gunning, stopping and popping, dodging and rolling and sliding and shooting. Giving melee its own dedicated button and governing it with a stamina meter is another smart move. And your co-op partner is actually helpful this time, with AI that keeps it from intrusively finishing every fight.
It sounds like the game's main problem are the QTEs. There are extensive shootout sequences between each of them, which is good, but it sounds like the QTEs result in frustration at times, and create for an uneven stop-and-go experience at others.
The other major flaw appears to be a simple matter of pacing, where the game apparently settles into dry spells of derivative gameplay. I do suspect people's mileage will vary in this respect: Your combat and mobility options have been expanded here to the point where you can create your own fun by simply throwing yourself into the thick of things with every trick at your disposal, from the all-new quick-shots and counters to dodging, rolling, sliding and shoulder-checking.
In other words, it's the difference between playing Vanquish as a cover-based shooter, picking your shots, or rocket-boosting into each and every battle. It's all in how you play.
Also, side note, seems weird for Kill Screen to criticize the plot coherence on grounds such as Leon boarding a flight after "murdering" the president (the president was a zombie, and it was in self-defense) and needing to find cranks to progress (a staple of -many- videogames). The game appears to be soap operatic in many respects, and I don't think we ought to take it as seriously as it takes itself. At least the voice acting is bearable now.
