I dont really get the love for demo. It is not bad, but still pretty boring. You are a stationary turret, pumping out demons - and your rotation doesnt really change a lot whether you have a single target fight, cleave, or AOE. Combined with only a few instant spells and not much movement, this spec is... meh for me.
I do get the idea of an almighty puppetmaster that shoots demons left and right, but mechanically, this isnt for me. In Legion, i played only Affliction and i really adored this spec - which now is only a shadow of its former self