To me Legion was a very fun expansion.
Sure it had its problems, like completely ruining the hunter class making me change my main to shaman for the first time ever, and some zones being rather subpar(Broken Shore), and the legiondaries being a grind for those who just wanted to raid. I was luckily not affected as heavily by that need as I was mostly playing casual in Legion. My guild died in WoD so I spent the majority of Legion just faffing about leveling alts and collecting transmogs and just having fun exploring the world, apart from a few raid pugs here and there.
I think if you were a casual player Legion was probably absolutely fantastic. If you were a raider then not so much due to the legiondaries problem.
Suramar, PvP dailies, secrets, mage tower, artifact skins, class mounts and class storylines offered me plenty to keep me busy and I enjoyed it a lot. I only unsubbed for a short period near the end due to burnout but returned to get most of the mage Tower skins before they went away for good.
I honestly miss the variety and amount of content we had in Legion over what we had in BfA and SL so far. We haven't had the variety in WQs Legion offered ever since for example. Variety is so important imo.
I'm still pissed that we can no longer experience the artifact weapons as they were when Legion was current. Never understood why the fresh weapons had to be depowered as well. Couldn't they have made them so they only worked in Legion zones? Leveling through Legion now is just a shadow of its former self.