There's nothing "realistic" or living about the different skins that enemies will have. Yes, you see different stuff... but that stuff isn't interest. Stormcloaks are just mooks. As are imperials. As are bandits. As are dragons. Killing a stormcloak isn't different from killing an imperial. The gameplay is the same. There's no deep or sophisticated interaction with them - you're either killing them or not.
Sure, stuff is new, but there's nothing particularly interesting about this "new" content. It's dynamic in that it isn't pre-scripted, but there's nothing to the dynamic content that they give you.
Skyrim doesn't give you variety. Sure, I can create different types of combat playstyles (assuming I don't play long enough to just get 80% of the skills), but all of the quests are identical, no one recognizes any difference in what I do, and there isn't that much difference in terms of the story.
We'll never see eye to eye on this, but as a matter of fact I just don't see that much variety in content.
Those encounters were just an example of one thing Skyrim does. It doesn't matter if we agree or not, as we merely have to let the numbers and the amount of hours people have spent on the game do the talking. We don't even need to include mods (which are a minority anyways as most don't play Skyrim on PC) to see that people spent a ridiculous amount of time in Skyrim compared to any other game. This is part of the reason why TES has always been regarded as the single player MMO because of how much time people spend, because there is always something to do or find. Your expectations or how you perceive that are purely a subjective matter.
Aye, that's a big advantage of semi-open world like Inquisition does. The game has deserts, snowy mountains, the hinterlands, a lush forest, marshes, and that's not all. Bethesda have less variety as a rule.
Morrowind may be the most varied and even then large parts of the map are still grey-brown wasteland, mixed with some lush greenlands in the south and a volcano. The quirky vegetation and architecture still makes it a great world to explore, but still.
Oblivion is green forests pretty much all over. Some marshes in the south, plains around Skingrad, some snow north, that's pretty much it.
Fallout 3 has grey-brown wasteland with a green tint, and... that's pretty much it. Oh yeah, Washington itself is less brown and more grey. Yay.
Fallout New Vegas is desert and more desert. And some differently colored rocks. Zion Canyon and the Divide in the DLCs look awesome however.
Skyrim is snow, mountains, snow on mountains, a forest in the south, and the semi-swampy regions around Solitude and Riften. Much of it is grey.
That's much less overall variety, which is inevitable when you attempt to cram an entire province or several US States in one level but still.
I think some of you folks need to go back and play through Skyrim, or Oblivion, or Morrowind. There is a lot more variety in the environment than what you are suggesting. DAI certainly isn't going to be more diverse just because they chopped up the world into zones.
Whether we talk about the Ashlands, Red Mountain, much of the vegetation near Seyda Neen, underwater content, Solstheim, Mournhold, Vivec City, Ebonheart, the various dungeons, ruins, caverns, crypts, etc.
One could argue Oblivion might be the least diverse? Most of it is just grasslands, forest, snow in the north, swamps in the south, ocean on the west, and then the Imperial City in the middle. Of course there are the various Ayleid ruins, forts and keeps, Oblivion gates, Shivering Isles, etc.
I don't even believe Fallout 3 should be included as it's a post-apocalyptic setting... Of course there isn't a lot of variety. Most of the environment is dead due to the nuclear fallout.
Fallout New Vegas wasn't developed by BGS, so that's irrelevant. Also, it's the Mojave Desert, so that more or less speaks for itself.
Skyrim by far is the most diverse. The various holds, the tundra, forest, swamps, hot springs, mountains, snow, hills and cliffs, grasslands, oceans, it has virtually every kind of ecosystem one would expect. Color palette and saturation does not mean a lack of variety. I agree Vanilla Skyrim was a bit subdued in terms of colors, but to argue there wasn't a wide variety of environments is silly.
The point is, true open world or just large environments, diversity in what one will experience will not differ from one to the other. That's entirely up to the art team and how creative they are in terms of developing the world.