To add to what Wubsie has said, it's impossible for any of us to tell you what you are going to like, and whether or not you're going to enjoy the end-game content in Legion. Every expansion, including the base game, has always had the same stuff to do:

1) Dungeons
2) Raids
3) PvP

At some point in the past you have probably enjoyed one or more of those activities in WoW or another MMORPG (end-game for all of the genre is practically the same), so this is likely going to be the same. Everyone has a different reason for multiboxing when they begin, and that can easily change once they reach end-game, but I always tell people to play the game with one character to see if they're going to enjoy it before jumping in with a full team.