Not entirely original. This concept was already extensively utilized in LotRO with skirmishes. Adding a storyline and missions for them was a good thing, but they serve little other than autopilot for more difficult to solo mobs. The only difference they present to gameplay is that instead of taking things on one at a time, you get multiple packs through the entire game.
A great feature for an RPG that as time goes on stands to be a weight that holds you down. It's a toss up based on personal preference, but it's not exactly a 'new' idea either.
Narrative in an MMO is not unique. Did they make you feel *more* involved than other games? Possibly. Vanilla WoW had flavors of this sprinkled in with class quests and so on, LotRO has your character completely woven into the events of the books, etc. I would consider their use to be refinement of an already established principle.
I can't argue with that.