As a history student, my focus is always on time periods and the events happening in them (which usually narrows things down to certain regions). Overall, the First Era has always had a place in my heart, mainly because so much has happened in that period that we actually have records for. Of course, the First Era is more than three times longer than the Second, which was twice as long as the Third, so the First Era's extremely long length (being more than twice as long as the next two eras put together) means that there is plenty of time for these things to happen. Still, my attention is almost always drawn to the very beginning and the very end of the era, mainly because of the rise of the Cyrodiilic Empires of those time periods. Something about Oblivion's presentation of Alessia and Reman caught my attention and held it. For some reason, I have always enjoyed fictional rulers with actual, literal divine support. Therefore, I very much enjoy reading about the rise of Tamriel's Dragonborn Emperors--and of course, the paradox/stable-time-loop-thing that the Dragonborn Emperors are supported by gods that they themselves created makes it all the more delicious.
And of course there are the politics involved with the rise and expansion of Cyrodiil, the decline of Skyrim, the sudden appearance of ALMSIVI and the subsequent isolation of a powerful Morrowind, and the slow marginalization of the Summerset Isles, which had already begun by the end of the Merethic, but accelerated noticeably in the First Era as Men began to wield more and more power over Tamriel.