The spec is by far the most difficult to play correctly out of the 3, and that is baseline without talents. We are still missing Thal'kiel's consumption, which looks like it will also be difficult to use 100% correctly. Talents like shadowfalme and summon Darkglare add even more buttons, furthering the complication, plus shadowflame has the extra dot to look out for and stack correctly. That's fine that those options exist for people that like a difficult spec with a high skill cap.
Most guides will strait away tell you that you should almost certainty pick up some specific addons and weak auras (like doomshards) to help you play and keep track of your normal rotation. I cant believe this is really intended class design with the entire demonology specialization. With difficult talent choices, sure, but I for one would like a little more strait forward, simple spec, where I can choose to talent into more difficult options.
I'm surprised that there aren't more options put into the talent tree to opt out of some of the difficulty, such as eliminating something like demonic empowerment or call dreadstalkers (though the latter option would take away from class flavor). Those are the 2 major spells adding a lot of difficulty to the basic rotation. You have an option to more or less make doom a spell you don't have to worry about manually applying. But maintaining doom is far from the most difficult thing about playing Demonology.
Probably already too late to see a major mechanic change (like removing a button from the rotation) this expac, which is pretty depressing because it hasn't even launched yet, but who knows?
TLDR: I would like to see demonic empowerment removed.