I am rather enthralled with the size of the Arcaneum and the wide variety of literature (alas, most under lock and key), but even more captivated by the first appearence of the Psijic order in any Elder Scrolls game. The Psijics are absolutely crucial to magic and to channeling the forces of Aetherium, so it was a light-shedding moment when one first appeared and spoke to me. I never realised that the Psijic order was still intact, just as I didn't realise the Blades are extinct (read "The rise and fall").
I havent yet finished the quests, but shall report back any interesting findings.