Well my biggest issue with RE5 and RE6 is that I think they changed too much. RE5 took too much inspiration from RE4's successors with its sunny environments, inflammatory setting, crazy amount of weapons, overabundance of QTEs, fighting hordes of The Sprinting Dead without changing RE4's method of stop-'n-pop, the cover shooting, the Majini begin using guns, and, last but not least, Sheva! Your faithful AI controlled partner, who I've heard horror stories about. 6 I didn't even bother as I love to say, but just watching that game I noticed problems, like opening the game with an explosion, mandatory walking segments, invisible walls, resetting the shoulder your camera is centred behind every time you enter a new area, incomprehensible semi-transparent HUD, and its juggling of FOUR different campaigns.
And both RE5 and RE6 take themselves way too seriously to be healthy.
And you have to remember, RE4 was a product of its environment. Classic RE was stagnating, Capcom was dissatisfied with REmake and ZERØ's sales, the Umbrella/Raccoon City story peaked in silliness at Code Veronica and the fixed angles and tank controls became highly stigmatized not just in RE, but any Survival Horror game. RE4 seemed to be the best course of action to deliver a fresh, new experience with solid combat and without alienating everybody.
And I know people who resent RE4 for being the gateway to RE5 and RE6 who weren't decrying RE4 as "the beginning of the end"
before 5's release.