Once you have a level 90 character you can speak with a giant Archmage Khadgar who then teleports you to Tanaan Jungle and the Assault on the Dark Portal.
(Missing Entry Cutscene and all voice acting =( )
-You are accompanied by Thrall, Lady Liadrin, Khadgar, Vinidicator Maraad, and a few others {note: will take screenshots and better list}
-You shut down a soul generator that is powering the Dark Portal, followed by stopping Gul'dan.
-You fall back to a different position and you rescue a good amount of Orcs and Draenei from camps.
-You save Drek'that and Ganar (perhaps different for alliance)
-You stop a blood ritual and manage to escape from Kilrogg.
-You end up in a mine and Khadgar collapses the entry way with rubble.
-You defeat the leaders of the mining operations and Ner'zhul ports in to fight you.
-Khadgar ports you out into a forge area
-You collect weapons for the orcs and draenei wiith you.
-You take control of a giant iron horde tank. The group of heroes you are with fight a giant battle versus the Iron Horde
-You blast them to hell and back and fire the canon. (Effectively taking out the the Dark Portal)
-The rest of the Iron Horde comes, you flee with the heroes to the docks. (Cutscene missing? Something is)
-You wind up with only Thrall, Khadgar, Drekthar in Frostfire Ridge.
-You quickly meet Durotan, and he trusts you because Drekthar tells him what has transpired
-You quickly come to a clearing, and you begin to set up your base (Garrison).
-Khadgar opens a portal to Ogrimmar (you cant take it)to reinforce you. Gazlowe followed by peons comes through. Theres quest to target trees for them to cut.
-High Overlord Saurfang comes through with troops! Huzzah!
-By this time i am well close to level 91. Not sure if this is intentional pacing of experience or not.
More notes later, I'm tired. Let me know if you guys want any specific details. I'm playing a premaid Male Orc Mage. Don't really want to answer class questions. More or less lore or tidbits.