We can't say for sure. The imagery in the video says "DRAGONS BE COMIN'" but alas, the dialogue cannot refer to dragons (as they were neither defeated, nor is their existence disputed).
And this is why I'm not convinced by the whole "Skyrims are the antagonists of Skyrim!" thing, because it seems obvious that the ones who are supposed to return, according to the dialog in the trailer, are NOT dragons, and it seems highly unlikely that whoever they are, they would NOT be the main enemies in the game. Not to say that I deny dragons will exist in the game, if Bethesda says they will, I wouldn't doubt they'll be there, I just doubt they'll be the main antagonists, but that still doesn't mean that we won't get to fight them, even if we maybe don't HAVE to to complete the main quest. And as to how fighting them will work, I really don't know. I'm sure they'll be big, of course, how big? I can't say, maybe similar in size to the Gate Keeper? It's impossible to say, but I highly doubt they'll be only human sized. And it is true that the combat system in Oblivion, or the one in Morrowind, for that matter, does not really handle extremely large foes that well, but since we know nothing about the combat system of Skyrim at this time, we can't be sure yet whether it will be better or not. So I'd say we just have to wait, and see.
I think it's safe to say, though, that we won't see Shadow of the Collossus style fights against dragons, at least, considering that ALL the combat in that game is against foes much larger than the player, and a large part of the appeal of it comes from how well it handles such fights, but in Skyrim, I'm sure most of the combat will be against enemies of similar size to the player, so it probably can't put nearly as much focus on that sort of thing.