I really liked Legion for a while, especially when I had some holiday time, because there's so much to do. I ran M+ with friends, did pug raids and WQs. However the sheer amount of things to do for your main is overwhelming. Over the years WoW has encouraged players to level alts (especially the expansions like WoD with less content). In previous expansions you could do your daily quests / daily heroic / mythic dungeons / raids and then you were done for the day / week; then it was time for your alt.
I am attached to my main but I also really enjoy playing my alts and I, personally, feel that when I'm playing on my alt I 'should' be playing my main. There is never a time when you're 'done' with your main. For some people this is great but it led to me playing the game an awful lot and content becoming incredibly repetitive as I was constantly doing the same grind on both characters (and wanted to level more but felt overwhelmed already).
Legion is a good expansion but it didn't keep me interested despite the amount of content.