I've put more hours into ESO than I'd admit to my GP, and I keep getting asked the same thing in our Discord: does any of it "count"? With TES VI's long shadow over everything, the question's stopped being academic. So here's my honest read on where ESO slots cleanly into the lore we knew from Arena through Skyrim, and where it visibly strains to make the join.
The Second Era setting actually helps
Putting ESO in 2E 582, during the Interregnum after the Reman line collapsed and before Tiber Septim, was the smartest structural choice ZeniMax made. It's a gap. Almost nothing in the single-player canon happens there in detail, so there's room to build without contradicting a beloved quest. The Three Banners War, Ebonheart Pact, Daggerfall Covenant, Aldmeri Dominion all clawing at the Ruby Throne, fills a power vacuum that the older lore only sketched. When ESO says Wulfharth or the Longhouse Emperors, it's filling blanks, not painting over them.
And a lot of it lands. Morrowind in ESO genuinely feels like Vvardenfell circa Tribunal-still-godlike, with the Tribunal at the height of their power instead of the fading husks Morrowind (2002) gives you. Going to Vvardenfell and seeing Vivec actually radiant, with Baar Dau still hanging overhead, is the kind of thing that earns the price of the chapter. The Clockwork City as Sotha Sil's literal mechanism-made-world is a faithful, gorgeous extrapolation of a guy the games only ever told you about secondhand.
Where the retcons bite
The friction shows up wherever ESO has to reconcile its scale with established timelines. The big fan argument is the Dwemer. Skyrim and Morrowind frame the Dwemer's disappearance (Red Mountain, 1E 700) as ancient, mysterious, total. ESO, set well after that, mostly respects it. But the sheer volume of intact, navigable Dwemer ruins and active mechanisms across the map makes "vanished lost civilization" feel a touch less haunting than it did in 2002. That's not a contradiction so much as tonal inflation.
Then there's the Daedric Princes, and this is where I think ESO does its best and shakes most. Molag Bal as the Coldharbour-bound main antagonist is excellent. The God of Schemes scheming, planar meld and all, lines up perfectly with his Mankar-Camoran-adjacent domination theme. Meridia, Mephala, Nocturnal, Clavicus Vile, all recognisably themselves. But the volume problem returns: when every zone has its Daedric crisis, the Princes start feeling like recurring raid bosses rather than the rare, reality-warping forces Oblivion treated them as. Sheogorath especially. ESO's Sheo is funny and well-written, but he's also, canonically, the post-Shivering-Isles Hero of Kvatch by the Fourth Era, which makes any Third or Second Era Sheogorath a continuity knot people genuinely argue about. The usual fan patch is "Mantling and CHIM mean identity isn't linear for a Prince," which is lore-accurate hand-waving but hand-waving all the same.
The other strain is geography and population. ESO lets you walk a continuous Tamriel that the older games chopped into province-sized chunks. Cyrodiil being a jungle (per pre-release Kirkbride lore) versus the temperate heartland Oblivion shipped is the cleanest example of the two canons quietly not matching, and ESO splits the difference rather than commit.
So is it canon enough for TES VI groundwork?
My take: yes, with a footnote. Bethesda has treated ESO as canon-adjacent. ZeniMax owns it, the broad strokes are blessed, and Hammerfell/High Rock lore from the Daggerfall Covenant is probably the single best modern reference point we have for whatever VI does with the Redguards and Bretons. But ESO is also written by committee across a decade, so the precise details are softer than a mainline game's. I'd trust it for who and where and broadly what; I wouldn't bet a forum argument on an exact date or a single NPC's fate. For groundwork on Hammerfell, the Alik'r, the Crowns-vs-Forebears split, Sai Sahan and company, it's the richest well we've got.
For the deeper rabbit hole, UESP's lore portal (https://en.uesp.net/wiki/Lore:Main_Page) is still the best-sourced cross-game reference, and our own Second Era lore thread has some good back-and-forth on the timeline gaps.
Here's my actual question for you lot: which single ESO retcon do you flatly refuse to accept into your personal canon. And is it the lore itself you object to, or just that it crowds out the mystery the older games left alone?