Yep, same here. I thought I'd completed the Mage's College main quests, but now I've found that there are some followup quests, so I'm not sure if I was really "finished". Regardless, they're quite fun. Hope the other factions have such engaging storylines.
Are you going to do the other factions on the same character? Or do them on a new one?
Can you even do all of them on one character? I mean it seems like I'd rather save the thieves guild quest for my sneaky kitty.