I love the setting, but from a bit of a distance -- I had a couple of the first edition books but none of the second edition stuff. I keep reading interesting posts about the game that rely on stuff I don't understand. Can anyone provide either a link to a summary, or a summary? A list of important books in the line might also be useful.
It's a tricky question to answer, because the Exalted metaplot ends at a specific time, and that specific end time hasn't changed since the 1e corebook. A few products have extended the Exalted timeline -- "Return of the Scarlet Empress" is the latest to do so -- but these generally provide possible futures. The First and Forsaken Lion doesn't necessarily conquer Autochthonia, the Sidereals don't necessarily unleash the Kukla, the Scarlet Empress doesn't necessarily enact a plot to render Creation and Hell one and the same.
What the Exalted metaplot has mostly been, then, is background. Setting elements that were implied to be X in a brief mention in an early sourcebook were expanded at length and revealed to be Y. Characters, power groups, whole regions were unveiled as unexpectedly awesome and tied to other setting elements in unexpected ways: the Haslanti League, like Halta, was a Lunar experiment. A Gold Faction Sidereal might share an office in Heaven with a Bronze Faction Sidereal. Astrology works along different principles than one might expect. The floating mountain in the far East isn't full of upsy-daisium, it's a derelict flying war machine.
Thus, there isn't a single good source to follow, because there isn't a single narrative throughline. The 2e core book hits a lot of the high points accreted over the course of the first edition, but it's presented as setting, not metaplot.
As has been mentioned above, the question is a tricky one. Officially, Exalted is less of a meta-plot, and more of a meta-setting. The authors have occasionally also stated - and in some books like Return of the Scarlet Empress made this explicit - that it's better viewed as a toolbox you can pick and choose from. For example, it's a much weirder game if you assume all the ways Creation might be destroyed right now are all going to happen.
The best way to get a decent view of the meta-setting is via the Core Book, the various Manuals of Exalted Power, and the Return of the Scarlet Empress. That gives you the whole scope of the game via the Core Book, and then that same scope viewed from the lens of each of the major player character type groups. The same setting is wildly different if you're talking about a Solar, a Sidereal or a Dragon Blood.
The other books in the line essentially flesh out little bits of that grand setting, focusing on a direction, or a particular aspect of the setting, like Sorcery or types of Demons. But the true heart of it is the Core Book and the Manuals of Exalted Power, which give you a good overview and "what is everyone up to?".