I am still torn about N'zoth. I do not think he is actually evil. The Old Gods are more like flesh machines that are constructed for a purpose by the Void Lords and do what this purpose requires without falling under the classification of good or evil. There is also reason to believe that he would aid us in our upcomming fight against Sylvanas and the Jailer since he does not profit from a dead planet anymore then we do.
Besides this, he clearly has a specific role for us in mind. He selected us (even before the U'unat fight) and somehow wanted us to succeed. At that point it could have been because he was planning his own release with Azshara, but he is still very ... uh... supportive I guess. He gives us corrupted gear to aid us and congratulates us every time we beat his minions in a Mythic + dungeon. He probably wants us as his prime soldiers in the comming Black Empire, much like Arthas wanted us to be his vanguard.
So while I know N'zoth's continued existance will be a problem for us, I kinda would like to explore the option of an alliance with him against Sylvanas/Jailer, as impossible as that is.
This is the difference between N'zoth and Sylvanas, he gives me pause and makes me think about what his goals actually are. He is not all powerful, in fact he is called the "weakest" of the Old Gods, so he has to rely on plots and influencing people. He is in a word "interesting". Sylvanas is just an overpowered megalomanic zombie that wants to murder everyone for her own benefit and carries a massive plot shield, so she cannot fail, she is no more interesting then Gargamel and will be killed off soon (but not soon enough)
So I think the Big Bad of the Expansion is N'zoth but only because he is the more interesting villain. The Horde is too foolish to be interesting, just a mindless mass of bodies that will attack anything their Warchief tells them to as long as they shout "For the Horde" loud enough.
Certainly most wars cost the lifes of innocents. But there is still a difference between colateral damage and targeting a civilian center for destruction AFTER you won the war. Sylvanas knew there were no soldiers left in Teldrassil and only civilians. But since she felt she had to teach Delaryn a lesson in how to kill hope, she murdered them all. These are the kinds of actions people do label as war crimes to this day.
See, funny thing. I had several Hordies tell me that the Purge of Dalaran with it's enormous death count of 5-10 Belfs counts as a genocide by the official diffinition of the word. By this logic the Horde has commited a ton of genocides. Gilneas, Hillsbrad, Theramore, Brennaden... the list goes on... point is, Teldrassil is in no way the only time the Horde commited genocide.
Every piece of earth the Horde takes under Sylvanas ends up blighted by her Forsaken. You literally meet a Forsaken in the pre-WF scenario on Darkshore that claims he has a forest to blight and you see Blight Wagons everywhere during the WF. You can't get earth much more scorched then turning it into a blighted wasterland where nothing but zombies can survive. Which already is new levels of stupid since the Horde has been whining for ages that they require fertile grounds to survive. Shame Sylvanas doesn't give a rat's ass about the Horde's living members.
No idea what you mean with Lordaeron? Do you mean with Arthas when he was controlled by the spirit of an Orc or when Sylvanas blighted her own capital? Both had nothing to do with the Alliance.
Argueably she brainwashed halve the leadership of the Horde, since Talryssa, Liadrin, Lor'themar, Baine, every Druid that ever existed in the Horde and even Firepaw should have cut her head off after Teldrassil, yet they were content watching where the Psycho Warchief was going with this.
But more to the point. Anduin basically Jedi Mind Tricked his guards to escape, he never caused any harm to them and gave them no orders that would put them in danger or violate their personal feelings. Sylvanas tortured Derek violently to break his spirit and intended for him to murder his mother, brother and his beloved sister. Basically she was gonna do to him what Arthas did to her.
If you cannot see the difference between these two acts then I don't know what to say, putting them on the same level is ridiculous.