Those who are unhappy with the current state of the game will always make vocal arguments against it. Whether this becomes widespread enough to become a broad consensus depends entirely on the quality of the expansion. Cataclysm and WoD got a large amount of criticism while they were current, because they are generally seen as weaker than the other expansions. It was rare you saw much nostalgic praise for Cataclysm prior to WoD arriving and supplanting it as the overall least favourite entry in the series.
TBC, Wrath, and Pandaria all had plenty of criticism levelled at them for being different from what came before, just as Legion will too. Every game will have its detractors. What's more useful to observe is whether that criticism holds much objective merit or not. There's a difference between the natural transitory unrest we got with TBC, Wrath, and Pandaria, and the widespread, strongly argued condemnation that WoD (and to a lesser extent Cataclysm) received.