McDonald's is having problems for the first time since it went public in the '60s - in the US I would attribute this to maturing taste. A NY Times editorial correctly identifies the chain's original appeal:

American companies exported this standardization to a world of consumers grateful for the promise of certainty - the certainty that a Coke or a Big Mac bought today will taste like one bought yesterday, not to mention one bought on another continent. But after a while, once the likes of McDonald's have elevated consumers' expectations, their omnipresence can become as unsettling as it is comforting. Fickle consumers turn away, seeking to reassert their individuality. That helps account for the ongoing fragmentation of consumer taste.

...Trouble is, at its core restaurants McDonald's acts as if its main problem were insufficiently low prices. So it is pushing its $1 "value menu" items with renewed vigor. Upgrading its offerings might make more sense. Otherwise, the chain's main product may soon generate nostalgia for a more innocent age when standardization was still a novelty and nobody could have foreseen a backlash against the ubiquitous.

Standardization is no longer a novelty here - we still want the safety but aren't willing to dip to the lowest common denominator to assure it anymore. And the world - for better or for worse - has come to see McDonald's as a symbol of American cultural domination, a victim of its own success. I don't see upgrading its fare as solving that riddle.