As they say, keep your friends close. I've enjoyed Arthas/Lich King lore since Warcraft 3 and wanted to experience more. I levelled a Rogue straight to level 55 and then logged off, created my DK and haven't looked back.
I still maintain a close friendship the the Lich King. I never really wanted to join the Horde, and my darkest day was having to kill him.
Now I just bide my time before being called upon once more.