Legion is remembered fondly for good initial content releases, strong raid tiers, Suramar, and interesting story beats. It also saw tons of complaining at the time for how dumb the idea that everyone is an artifact weilding commander of their entire class's collective efforts. This isn't an issue of overall quality of expansions, it's a debate about the level of narrative focus given to the player character, spanning from being a no name unimportant soldier doing small tasks to being the chosen prophesized savior of a cosmic realm. Legion is on the far bad end of expansions for this aspect.