Impressive looking, maybe. But as an actual character with motivations and power to alter the world? Hardly. I never once felt threatened by him or his dragons. For such a powerful intelligent race, they are awfully disorganized, and he keeps a rather long chain to his servitors.
Why did he never call his risen priests and draugr, and other dragons to lead devastating attacks and claim cities in his name converting more to his worship? Why did he never think to engage us in combat at any point during his dragon resurrections, if he knew we were powerless to stop him before acquiring dragonrend? Why did he save us at Helgen? Why did he not bother to try and convince others it would be in their best interest to stand with him than against him?
His entire character is literally set up to fail, as he makes countless "cartoon villain" mistakes in a row. It's absolutely pathetic. A good villain should make you hate them, a good antagonist could make you love or hate them depending on their motivations and drives, Alduin however, is neither as he prompts only indifference from me.
You could just as easily say that Alduin was doomed to fail when your character survived getting his head chopped off, Alduin's destiny was doom this time around.
Indeed, if one consider's P-nax, it could also be said that the line between villain and hero has been considerably blurred in Skyrim. Just read a few posts about dragons, there is much sympathy for them now.
Skyrim didn't have too many boundaries, no set black and whites, it was a sea of grey in more ways than one.
I've found that those are normally the more difficult stories to interpret, or write for that matter, and as absolutes go... they tend to be pretty predictable.