I had to look up what you meant by Adventure / Exploration, and I'm not quite sure I understand it even now. Like a game hinging on adventure and exploration?

ESO is an MMORPG. A Role-Playing Game. So the quests you experience and the choices you make, such as they are, impact your character. The depth of your gaming experience is determined by the depth of your roleplaying.

That's something that didn't change from before to after One Tamriel. The method of progression changes but the ability of players to experience and roleplay their way through the world didn't change except to become more expansive and less hemmed in by a leveled railroad.

As for the adventure and exploration, I'd like to compare it to some past Elder Scrolls games.

TES III: Morrowind probably had the highest quotient of adventure/exploration because its world was not leveled. Enemies in ruins and delves were largely pre-placed, so it was easy to wander into something you had no hope of beating...but it you could beat it, can you say a full suit of ebony armor at level 10?! And so on. Oh, and the complete lack of quest markers was surely a boon to exploration...you got to explore the same patch of Ashlands for the tenth time looking for the fork at the burnt tree that marked the kwama mine...okay, now I'm griping. If you wanted exploration and the ability to never know what was around the next corner, Morrowind is your game. It was also a game with a lot of "go there-do/kill/steal this" quests that made up a large part of its Guild and House storylines, so there's some unevenness going on there.

TES IV: Oblivion was a big step down in exploration with its leveled world and small selection of cave/build layouts. Oblivion was a big step up in the scale of the world and the action of its quests. Where Morrowind is all about the past and its impact on the present, Oblivion is all about your actions now and it brings a commendable sense of urgency to your questing. Oblivion also really fleshes out the Guild questlines, giving them a compelling story to go with all the go there - do/kill/steal this fetch quests. The DLC really add the exploration quotient that the main game lacked. The Knights of the Nine has some puzzle solving (Hey, its nothing special but its slightly better than Skyrim's "puzzles") and the Shivering Isles

TES V: Skyrim presents an active world with troubles of its own. You get thrown into it and handed the power to change everyone's lives, but they've got their own things going on. The (mostly leveled) world is still your oyster and you can explore anywhere you want, but there's still a sense of danger from poking your nose into places you can't handle even though you won't get fantastic rewards. There's creative environments to explore and the ruins/caves/tombs design team took a huge leap forward from Oblivion. The Guild Quests make you an active participant with lots of sneaking, fighting, and killing in all of them while keeping Oblivion's emphasis on an engaging storyline. The puzzles are severely lacking in Skyrim, often needing nothing more than a glance at a dragon claw or reading a book to figure them out. The Dragonborn and Dawnguard DLC add more interesting environments and higher level enemies.

Now for ESO. ESO's world is both larger and smaller than Skyrim's. The world as a whole is much bigger. Individual delves are much smaller, feeling more akin to Oblivion's small selection of layouts. Above-ground environments are much more tightly packed. Where Skyrim could give us views of Whiterun's wide-open grassy plains, ESO has to pack their content in using mountains and impassable terrain to hide how closely packed all the content is. ESO's questing is strong on the Main Quest and Alliance Quests quests, but turns pretty formulaic on the regional sidequests with some notable exceptions. The DLC add new zones to explore and new Guilds to quest with. Group Dungeons generally do a good job of melding story with action, where the "puzzle-solving" isn't actual puzzles but its figuring out mechanics and how to beat them. ESO, even more than the other Elder Scrolls, allows you to engage with the world at your own pace now that One Tamriel dropped. If you want to roleplay your Vestige, there's plenty of meat in the many questlines. If you just want to grind to CP 160, roleplaying is entirely optional.

So for me, ESO hits pretty much the same mark as Morrowind, Oblivion, and Skyrim. Its not the best in all categories nor the worst. The roleplaying experience is there if you want it to be and rewards the depth of immersion you reach with a given character. I'd put the questing on the same level as Morrowind. The quests with actual story are great, the rest are formulaic. The adventure/exploration in the overland world is there - probably on about the same level of Oblivion. The environments are pretty but there's not a lot of meat there. The adventure/exploration in the group dungeons is there - probably on the same level as Skyrim, with a very good blend of story, scene, and action.