If memory serve's right, High Rock and Hammerfell both appeared in TES:II - Daggerfall, Vvardenfell and Morrowind were both in TES:III - Morrowind.
Vvardenfell was an island in the middle of the Inner Sea (a large bay) within Morrowind, and considered a part of the province. Only a small portion of the one province was featured in the game. We never got to set foot on the larger portions of the province (except in the quarantined inner courtyard of the city of Mournhold, and on the small, remote island of Solstheim), although the Tamriel Rebuilt team is modding that in as we speak. So far, two of the expected 6-7 installments are available as very playable betas (if you're playing on PC), and are surprisingly close to the original game in concept, art styles, and lore, while still providing fresh sights and challenges.
I believe that Daggerfall only touched on the edge of Hammerfell (although I have yet to get DF working properly, via DOS emulator on my computer, so I'm not positive), so it appears we only got a poorly rendered glimpse of a narrow sliver of it.
Like Morrowind, with its swamps along the Bitter Coast, fertile Ascadian Isles plantations, rocky West Gash highlands, lush Grazelands, dreary Ashlands, and odd mushroom-tree Azura's Coast areas, both Elsweyr and Hammerfell have diverse ecologies. Elsweyr includes sandy and stony deserts, as well as tropical jungles. Hammerfell includes both sandy and stony deserts and fertile or irrigated plains with cornfields. The criticisms are just as bad and inaccurate as "Skyrim is just snowy mountains".
The swamps of Black Marsh could be far more varied than one can imagine, with swamps, jungles, rivers, sudden rocky ridges or volcanic mounds rising abruptly from the marshy soil, and occasional patches of firm, dry ground suitable for the scattered inhabitants to build isolated villages on, all infested with an abundance of varied plants and animals the likes of which we have yet to see. The game could be "naturally levelled" by having the character starting in the thin habitable coastal strips and a few well-patrolled trails between them, and gradually be able to venture farther and farther into the harsh and wild interior as they progress, so it can be tackled according to when you feel "ready", instead of having the difficulty imposed on you by the levelling/scaling system. I HATE the excessive levelling and scaling in the newer games.
My first choice for the next installment would be Black Marsh (Argonia), but Elsweyr comes fairly close behind that. Hammerfell, Valenwood, or Summerset Isles would be fine with me as well. I don't really want to go back to another "generic" province like High Rock, and there's too much unexplored area on Tamriel to venture to Akavir or Atmora yet.