Some people thought they were the Akaviri (And the Dragons). Me included.
If it's not a spoiler, it should end speculation of who they are. These are (giant) dragons, clearly enough.
the Giants began to come down from the mountains again. And they were a bit different than we Nords remembered, or perhaps we had forgotten much, but they would not speak to us anymore-- they would only smile in their lazy way, stomp over, and take our stuff.Sounds like dragon shenanigans, to me: virgins, treasure, people to eat, good ol' orderly society, you-name-it. They can be lazy about it, because they only fear "the one," and it takes a while for the one to solve problems, doesn't it? It always takes a journey.
I suspect it'll be up to the player how the Dovahkiin pleases everyone and solves the dragon dilemma. Given the nature of the Dragonborn, being http://www.imperial-library.info/content/morrowind-arcturian-heresy, we should have plenty of freedom: destroyer and creator, a la http://www.learntarot.com/maj12.htm.