Level your new character through old content in a new way. Classic zones scale up to 40 levels, while expansion content can be rearranged to your liking, allowing you to level 60-70 in Warlords of Draenor content for example.
Plunder islands filled with random threats in groups of three and race against enemy players to complete objectives.
Fight against other players to create bases and lay siege against other player fortifications in the siege maps inspired by Warcarft RTS games.
And finally... Join social groups across server. Also, brand new PVP instance grouping, where every player is joined in a pool after flagging for PVP inside of cities and fight against each other for world pvp rewards.