What? Legion was awesome from the start. WOTLK was awesome from the start. Both had awesome reviews from the start.
MOP was awesome after 5.1 (rep gates removed).
Cata, WoD, and BFA sucked at launch and the first two continued to suck throughout their respective life cycles.
BC and Vanilla are the only expansions that have been deemed "awesome in hindsight" (in reality, they were both some great ideas with some total shit; if you disagree, I wonder how many texts you got at 3 AM because a world boss spawned).
So which expansions do you mean by "every"?