You do know there are waterfalls in Oblivion, even Morrowind, too... that moves?
But yah, Skyrim got more animations for everything and that makes the world feel less static and lifeless.
Which are all obvious additions. Do people have such low faiths in Bethesda that they don't expect them to attempt to make the world feel less like a frozen picture frame and rather moreso in motion?
If Bethesda's good at something it's usually world building. Then there's the dungeons themselves Hopefully having more people and less dungeons means that side of gameplay won't be stale, ie. Same cave for 60 dungeons.
Story, writing, VO writing and quality, story, writing, VO writing and quality. Good luck Beth. You'll need it.