Oblivion's http://images.uesp.net//a/ad/OB-npc-Mankar_Camoran.jpg appeared more often, but still never committed any atrocities with his own hands, and his generic appearance made him less intimidating than Dagoth Ur. Similarly, the http://images.uesp.net/2/21/OB-NPC-Agents.jpg weren't as visibly twisted as the 5th house, which removed the horror element from the antagonists that greatly aided Morrowind. http://images.uesp.net//c/c9/Mehrunes_Dagon.jpg never spoke and only appeared, once again, at the end of the game, and he's dispatched rather quickly.
The Guild villains actually fared a bit better. The Dark Brotherhood at least gave the sense of a true monster lurking in your midst, Mannimarco attacked one of the more pleasant groups of mages you had met, and the Blackwood Company turned YOU into the monster, making your revenge against them all the more sweet.
Now, with Skyrim's Dragons revealed to be our new foes, I'm cautiously optimistic that they will be done well. I'm a bit worried by the lack of dialogue from them, which is essential to forming a good villain, but Todd has hinted that some dragons speak English, and I'm certain Alduin will be amongst them. I'm hoping that other Main Quest dragons, presumably Alduins most trusted minions, will each make for interesting antagonists whose presence will be felt throughout the main quest, not just at its climix.
The whole "dragons attack villages" concept could certainly allow Alduin to play a more active role in the game than previous antagonists, destroying innocent people before your eyes and driving home the point that he must be stopped. I think that seeing him once or twice over the course of the MQ, being left in awe of his power and cruelty, should be enough to heighten the suspense for the inevitable final battle with him.
What do you guys think? Both of the villains in previous TES games, and of the possibilities for Alduin to rise above them.