Well, Mehrunes Dagon not having much of an apparent motivation for wanting to destroy anything sort of makes sense, being the Prince of Destruction and all that, it's pretty much in his nature. The problem is that we didn't really get a good look at the mortal villain's motivation, I can understand a god of destruction wanting to destroy the world, but a mortal who would be destroyed with the world needs some sort of motivation, and Mankar Camoran really just came off as insane, or at the very least, extreme in his views, which explains why he would support Mehrunes Dagon, I guess, but it doesn't adress why people would be loyal to him.
But really, I don't expect Alduin to have much in the way of a motivation beyond "It's what I do." either. He doesn't strike me as the kind of antagonist that is likely to have a very complex motivation, though I could be mistaken. But that doesn't necessarily mean that he can't make for a good story, just that you have to either introduce other antagonists with more nuanced motives, or you have to build the appeal of the story on something other than having a complex villain. While certainly, the villain of a story is an important aspect of it since, at least in the sort of stories that rely on villains, because the villain drives the central conflict of the story, having a complex villain isn't the only way to make a good story, it's just that having a good villain is a very effective way to enhance a story, and a bad one can often ruin it (Though when I say a bad villain, I don't necessarily mean a simple one. Some villains are fairly one dimmensional when you get down to it, but they still work because they fulfill their purpose in the story very well.)
Any story can be made to seem one-dimensional and simplistic, if summarised in a certain way. Bonus points for naming these literary works (but beware of spoilers):
That's also a pretty good point. People like to praise Morrowind's main quest here, yet I could very easily sum it up thusly: The evil god Dagoth Ur threatens to enslave the land of Morrowind, and only the reincarnation of the a Dunmer hero, whose coming was foretold by an ancient prophecy, can stop him. Do you have what it takes to fulfill your destiny and become the Nerevarine?
Sounds pretty simple, doesn't it? Yet whether you like the story of Morrowind or not (I think it has some pretty good ideas and a good background but could have been told better, myself.) I think you'll agree than there's more to it than what I just said would indicate.
Durrr, Alduin smash.
Hah, now that I think about it Alduin and his dragons seem a lot like the reapers in Mass Effect - since Alduin also likes to come in every
X years and wipe everything out...
Hmm... http://www.youtube.com/watch?v=li5aDU9280c&feature=BF&list=PLED411B83F57B0A3C&index=3
Sorry, I couldn't resist doing that when I saw that statement.