I thought the story for Cata was bad. What with Deathwing acting like a disaffected teenager. Not to mention the whole last raid where we fought his bacne and toenails.
I thought the story for MoP was meh. Then Garrosh went off the deep end and meh turned to /facepalm
I thought the story for WoD was bad. So many plot holes throughout the expansion.
I thought the story for Legion was bad. To include some of the sub-plots (DK’s attacking the Paladin class hall).
BFA takes the cake.